diff --git a/app/builders/contact_inbox_builder.rb b/app/builders/contact_inbox_builder.rb
index ffa45db2e..4d51700a8 100644
--- a/app/builders/contact_inbox_builder.rb
+++ b/app/builders/contact_inbox_builder.rb
@@ -12,50 +12,11 @@ class ContactInboxBuilder
   private
 
   def generate_source_id
-    case @inbox.channel_type
-    when 'Channel::TwilioSms'
-      twilio_source_id
-    when 'Channel::Whatsapp'
-      wa_source_id
-    when 'Channel::Email'
-      email_source_id
-    when 'Channel::Sms'
-      phone_source_id
-    when 'Channel::Api', 'Channel::WebWidget'
-      SecureRandom.uuid
-    else
-      raise "Unsupported operation for this channel: #{@inbox.channel_type}"
-    end
-  end
-
-  def email_source_id
-    raise ActionController::ParameterMissing, 'contact email' unless @contact.email
-
-    @contact.email
-  end
-
-  def phone_source_id
-    raise ActionController::ParameterMissing, 'contact phone number' unless @contact.phone_number
-
-    @contact.phone_number
-  end
-
-  def wa_source_id
-    raise ActionController::ParameterMissing, 'contact phone number' unless @contact.phone_number
-
-    # whatsapp doesn't want the + in e164 format
-    @contact.phone_number.delete('+').to_s
-  end
-
-  def twilio_source_id
-    raise ActionController::ParameterMissing, 'contact phone number' unless @contact.phone_number
-
-    case @inbox.channel.medium
-    when 'sms'
-      @contact.phone_number
-    when 'whatsapp'
-      "whatsapp:#{@contact.phone_number}"
-    end
+    ContactInbox::SourceIdService.new(
+      contact: @contact,
+      channel_type: @inbox.channel_type,
+      medium: @inbox.channel.try(:medium)
+    ).generate
   end
 
   def create_contact_inbox
@@ -91,7 +52,7 @@ class ContactInboxBuilder
 
   def new_source_id
     if @inbox.whatsapp? || @inbox.sms? || @inbox.twilio?
-      "whatsapp:#{@source_id}#{rand(100)}"
+      "#{@source_id}#{rand(100)}"
     else
       "#{rand(10)}#{@source_id}"
     end
diff --git a/app/controllers/api/v1/accounts/contacts/contact_inboxes_controller.rb b/app/controllers/api/v1/accounts/contacts/contact_inboxes_controller.rb
index d985c8a73..bde9a4f0c 100644
--- a/app/controllers/api/v1/accounts/contacts/contact_inboxes_controller.rb
+++ b/app/controllers/api/v1/accounts/contacts/contact_inboxes_controller.rb
@@ -9,6 +9,8 @@ class Api::V1::Accounts::Contacts::ContactInboxesController < Api::V1::Accounts:
       source_id: params[:source_id],
       hmac_verified: hmac_verified?
     ).perform
+  rescue ArgumentError => e
+    render json: { error: e.message }, status: :unprocessable_entity
   end
 
   private
diff --git a/app/javascript/dashboard/components-next/NewConversation/helpers/composeConversationHelper.js b/app/javascript/dashboard/components-next/NewConversation/helpers/composeConversationHelper.js
index 57e819245..45abef1e0 100644
--- a/app/javascript/dashboard/components-next/NewConversation/helpers/composeConversationHelper.js
+++ b/app/javascript/dashboard/components-next/NewConversation/helpers/composeConversationHelper.js
@@ -25,6 +25,11 @@ export const generateLabelForContactableInboxesList = ({
     channelType === INBOX_TYPES.TWILIO ||
     channelType === INBOX_TYPES.WHATSAPP
   ) {
+    // Handled separately for Twilio Inbox where phone number is  not mandatory.
+    // You can send message to a contact with Messaging Service Id.
+    if (!phoneNumber) {
+      return name;
+    }
     return `${name} (${phoneNumber})`;
   }
   return name;
diff --git a/app/javascript/dashboard/components-next/NewConversation/helpers/specs/composeConversationHelper.spec.js b/app/javascript/dashboard/components-next/NewConversation/helpers/specs/composeConversationHelper.spec.js
index 3de1fad0d..37ae5fe29 100644
--- a/app/javascript/dashboard/components-next/NewConversation/helpers/specs/composeConversationHelper.spec.js
+++ b/app/javascript/dashboard/components-next/NewConversation/helpers/specs/composeConversationHelper.spec.js
@@ -8,8 +8,8 @@ vi.mock('dashboard/api/contacts');
 describe('composeConversationHelper', () => {
   describe('generateLabelForContactableInboxesList', () => {
     const contact = {
-      name: 'John Doe',
-      email: 'john@example.com',
+      name: 'Priority Inbox',
+      email: 'hello@example.com',
       phoneNumber: '+1234567890',
     };
 
@@ -19,7 +19,7 @@ describe('composeConversationHelper', () => {
           ...contact,
           channelType: INBOX_TYPES.EMAIL,
         })
-      ).toBe('John Doe (john@example.com)');
+      ).toBe('Priority Inbox (hello@example.com)');
     });
 
     it('generates label for twilio inbox', () => {
@@ -28,7 +28,14 @@ describe('composeConversationHelper', () => {
           ...contact,
           channelType: INBOX_TYPES.TWILIO,
         })
-      ).toBe('John Doe (+1234567890)');
+      ).toBe('Priority Inbox (+1234567890)');
+
+      expect(
+        helpers.generateLabelForContactableInboxesList({
+          name: 'Priority Inbox',
+          channelType: INBOX_TYPES.TWILIO,
+        })
+      ).toBe('Priority Inbox');
     });
 
     it('generates label for whatsapp inbox', () => {
@@ -37,7 +44,7 @@ describe('composeConversationHelper', () => {
           ...contact,
           channelType: INBOX_TYPES.WHATSAPP,
         })
-      ).toBe('John Doe (+1234567890)');
+      ).toBe('Priority Inbox (+1234567890)');
     });
 
     it('generates label for other inbox types', () => {
@@ -46,7 +53,7 @@ describe('composeConversationHelper', () => {
           ...contact,
           channelType: 'Channel::Api',
         })
-      ).toBe('John Doe');
+      ).toBe('Priority Inbox');
     });
   });
 
diff --git a/app/services/base/send_on_channel_service.rb b/app/services/base/send_on_channel_service.rb
index 298f60962..58f225ef0 100644
--- a/app/services/base/send_on_channel_service.rb
+++ b/app/services/base/send_on_channel_service.rb
@@ -12,8 +12,10 @@ class Base::SendOnChannelService
 
   def perform
     validate_target_channel
+
     return unless outgoing_message?
     return if invalid_message?
+    return if invalid_source_id?
 
     perform_reply
   end
@@ -49,6 +51,29 @@ class Base::SendOnChannelService
     message.private? || outgoing_message_originated_from_channel?
   end
 
+  def invalid_source_id?
+    return false unless channels_to_validate?
+
+    return false if contact_inbox.source_id == expected_source_id
+
+    message.update!(status: :failed, external_error: I18n.t('errors.channel_service.invalid_source_id'))
+    true
+  end
+
+  def expected_source_id
+    ContactInbox::SourceIdService.new(
+      contact: contact,
+      channel_type: inbox.channel_type,
+      medium: inbox.channel.try(:medium)
+    ).generate
+  rescue ArgumentError
+    nil
+  end
+
+  def channels_to_validate?
+    inbox.sms? || inbox.whatsapp? || inbox.email? || inbox.twilio?
+  end
+
   def validate_target_channel
     raise 'Invalid channel service was called' if inbox.channel.class != channel_class
   end
diff --git a/app/services/contact_inbox/source_id_service.rb b/app/services/contact_inbox/source_id_service.rb
new file mode 100644
index 000000000..995bc37a9
--- /dev/null
+++ b/app/services/contact_inbox/source_id_service.rb
@@ -0,0 +1,55 @@
+class ContactInbox::SourceIdService
+  pattr_initialize [:contact!, :channel_type!, { medium: nil }]
+
+  def generate
+    case channel_type
+    when 'Channel::TwilioSms'
+      twilio_source_id
+    when 'Channel::Whatsapp'
+      wa_source_id
+    when 'Channel::Email'
+      email_source_id
+    when 'Channel::Sms'
+      phone_source_id
+    when 'Channel::Api', 'Channel::WebWidget'
+      SecureRandom.uuid
+    else
+      raise ArgumentError, "Unsupported operation for this channel: #{channel_type}"
+    end
+  end
+
+  private
+
+  def email_source_id
+    raise ArgumentError, 'contact email required' unless contact.email
+
+    contact.email
+  end
+
+  def phone_source_id
+    raise ArgumentError, 'contact phone number required' unless contact.phone_number
+
+    contact.phone_number
+  end
+
+  def wa_source_id
+    raise ArgumentError, 'contact phone number required' unless contact.phone_number
+
+    # whatsapp doesn't want the + in e164 format
+    contact.phone_number.delete('+').to_s
+  end
+
+  def twilio_source_id
+    raise ArgumentError, 'contact phone number required' unless contact.phone_number
+    raise ArgumentError, 'medium required for Twilio channel' if medium.blank?
+
+    case medium
+    when 'sms'
+      contact.phone_number
+    when 'whatsapp'
+      "whatsapp:#{contact.phone_number}"
+    else
+      raise ArgumentError, "Unsupported Twilio medium: #{medium}"
+    end
+  end
+end
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 4a66a4bc2..27ba48cba 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -67,6 +67,9 @@ en:
       invalid_message_type: 'Invalid message type. Action not permitted'
     slack:
       invalid_channel_id: 'Invalid slack channel. Please try again'
+    channel_service:
+      invalid_source_id: "This conversation may have originally belonged to a different contact but is now showing here due to a merge or update. You won't be able to continue this conversation. Please create a new conversation to proceed."
+
     inboxes:
       imap:
         socket_error: Please check the network connection, IMAP address and try again.
diff --git a/spec/builders/contact_inbox_builder_spec.rb b/spec/builders/contact_inbox_builder_spec.rb
index f0e3deb31..b6519f130 100644
--- a/spec/builders/contact_inbox_builder_spec.rb
+++ b/spec/builders/contact_inbox_builder_spec.rb
@@ -59,7 +59,7 @@ describe ContactInboxBuilder do
             contact: contact,
             inbox: twilio_inbox
           ).perform
-        end.to raise_error(ActionController::ParameterMissing, 'param is missing or the value is empty: contact phone number')
+        end.to raise_error(ArgumentError, 'contact phone number required')
       end
     end
 
@@ -117,7 +117,7 @@ describe ContactInboxBuilder do
             contact: contact,
             inbox: twilio_inbox
           ).perform
-        end.to raise_error(ActionController::ParameterMissing, 'param is missing or the value is empty: contact phone number')
+        end.to raise_error(ArgumentError, 'contact phone number required')
       end
     end
 
@@ -174,7 +174,7 @@ describe ContactInboxBuilder do
             contact: contact,
             inbox: whatsapp_inbox
           ).perform
-        end.to raise_error(ActionController::ParameterMissing, 'param is missing or the value is empty: contact phone number')
+        end.to raise_error(ArgumentError, 'contact phone number required')
       end
     end
 
@@ -232,7 +232,7 @@ describe ContactInboxBuilder do
             contact: contact,
             inbox: sms_inbox
           ).perform
-        end.to raise_error(ActionController::ParameterMissing, 'param is missing or the value is empty: contact phone number')
+        end.to raise_error(ArgumentError, 'contact phone number required')
       end
     end
 
@@ -290,7 +290,7 @@ describe ContactInboxBuilder do
             contact: contact,
             inbox: email_inbox
           ).perform
-        end.to raise_error(ActionController::ParameterMissing, 'param is missing or the value is empty: contact email')
+        end.to raise_error(ArgumentError, 'contact email required')
       end
     end
 
diff --git a/spec/services/contact_inbox/source_id_service_spec.rb b/spec/services/contact_inbox/source_id_service_spec.rb
new file mode 100644
index 000000000..94fe8a384
--- /dev/null
+++ b/spec/services/contact_inbox/source_id_service_spec.rb
@@ -0,0 +1,117 @@
+require 'rails_helper'
+
+RSpec.describe ContactInbox::SourceIdService do
+  let(:contact) { create(:contact, email: 'test@example.com', phone_number: '+1234567890') }
+
+  describe '#generate' do
+    context 'when channel is TwilioSms' do
+      let(:channel_type) { 'Channel::TwilioSms' }
+
+      context 'with SMS medium' do
+        subject { described_class.new(contact: contact, channel_type: channel_type, medium: 'sms') }
+
+        it 'returns phone number as source id' do
+          expect(subject.generate).to eq(contact.phone_number)
+        end
+      end
+
+      context 'with WhatsApp medium' do
+        subject { described_class.new(contact: contact, channel_type: channel_type, medium: 'whatsapp') }
+
+        it 'returns whatsapp prefixed phone number as source id' do
+          expect(subject.generate).to eq("whatsapp:#{contact.phone_number}")
+        end
+      end
+
+      context 'with invalid medium' do
+        subject { described_class.new(contact: contact, channel_type: channel_type, medium: 'invalid') }
+
+        it 'raises ArgumentError' do
+          expect { subject.generate }.to raise_error(ArgumentError, 'Unsupported Twilio medium: invalid')
+        end
+      end
+
+      context 'without medium' do
+        subject { described_class.new(contact: contact, channel_type: channel_type) }
+
+        it 'raises ArgumentError' do
+          expect { subject.generate }.to raise_error(ArgumentError, 'medium required for Twilio channel')
+        end
+      end
+    end
+
+    context 'when channel is Whatsapp' do
+      subject { described_class.new(contact: contact, channel_type: 'Channel::Whatsapp') }
+
+      it 'returns phone number without + as source id' do
+        expect(subject.generate).to eq(contact.phone_number.delete('+'))
+      end
+
+      context 'when contact has no phone number' do
+        let(:contact) { create(:contact, phone_number: nil) }
+
+        it 'raises ArgumentError' do
+          expect { subject.generate }.to raise_error(ArgumentError, 'contact phone number required')
+        end
+      end
+    end
+
+    context 'when channel is Email' do
+      subject { described_class.new(contact: contact, channel_type: 'Channel::Email') }
+
+      it 'returns email as source id' do
+        expect(subject.generate).to eq(contact.email)
+      end
+
+      context 'when contact has no email' do
+        let(:contact) { create(:contact, email: nil) }
+
+        it 'raises ArgumentError' do
+          expect { subject.generate }.to raise_error(ArgumentError, 'contact email required')
+        end
+      end
+    end
+
+    context 'when channel is SMS' do
+      subject { described_class.new(contact: contact, channel_type: 'Channel::Sms') }
+
+      it 'returns phone number as source id' do
+        expect(subject.generate).to eq(contact.phone_number)
+      end
+
+      context 'when contact has no phone number' do
+        let(:contact) { create(:contact, phone_number: nil) }
+
+        it 'raises ArgumentError' do
+          expect { subject.generate }.to raise_error(ArgumentError, 'contact phone number required')
+        end
+      end
+    end
+
+    context 'when channel is Api' do
+      subject { described_class.new(contact: contact, channel_type: 'Channel::Api') }
+
+      it 'returns a UUID as source id' do
+        allow(SecureRandom).to receive(:uuid).and_return('uuid-123')
+        expect(subject.generate).to eq('uuid-123')
+      end
+    end
+
+    context 'when channel is WebWidget' do
+      subject { described_class.new(contact: contact, channel_type: 'Channel::WebWidget') }
+
+      it 'returns a UUID as source id' do
+        allow(SecureRandom).to receive(:uuid).and_return('uuid-123')
+        expect(subject.generate).to eq('uuid-123')
+      end
+    end
+
+    context 'when channel is unsupported' do
+      subject { described_class.new(contact: contact, channel_type: 'Channel::Unknown') }
+
+      it 'raises ArgumentError' do
+        expect { subject.generate }.to raise_error(ArgumentError, 'Unsupported operation for this channel: Channel::Unknown')
+      end
+    end
+  end
+end
diff --git a/spec/services/sms/send_on_sms_service_spec.rb b/spec/services/sms/send_on_sms_service_spec.rb
index d2dc1f24a..52c5d89b1 100644
--- a/spec/services/sms/send_on_sms_service_spec.rb
+++ b/spec/services/sms/send_on_sms_service_spec.rb
@@ -5,8 +5,9 @@ describe Sms::SendOnSmsService do
     context 'when a valid message' do
       let(:sms_request) { double }
       let!(:sms_channel) { create(:channel_sms) }
-      let!(:contact_inbox) { create(:contact_inbox, inbox: sms_channel.inbox, source_id: '+123456789') }
-      let!(:conversation) { create(:conversation, contact_inbox: contact_inbox, inbox: sms_channel.inbox) }
+      let!(:contact) { create(:contact, phone_number: '+123456789') }
+      let!(:contact_inbox) { create(:contact_inbox, contact: contact, inbox: sms_channel.inbox, source_id: '+123456789') }
+      let!(:conversation) { create(:conversation, contact_inbox: contact_inbox, inbox: sms_channel.inbox, contact: contact) }
 
       it 'calls channel.send_message' do
         message = create(:message, message_type: :outgoing, content: 'test',
diff --git a/spec/services/twilio/send_on_twilio_service_spec.rb b/spec/services/twilio/send_on_twilio_service_spec.rb
index beae54b57..af74a46e7 100644
--- a/spec/services/twilio/send_on_twilio_service_spec.rb
+++ b/spec/services/twilio/send_on_twilio_service_spec.rb
@@ -13,9 +13,11 @@ describe Twilio::SendOnTwilioService do
   let!(:twilio_whatsapp) { create(:channel_twilio_sms, medium: :whatsapp, account: account) }
   let!(:twilio_inbox) { create(:inbox, channel: twilio_sms, account: account) }
   let!(:twilio_whatsapp_inbox) { create(:inbox, channel: twilio_whatsapp, account: account) }
-  let!(:contact) { create(:contact, account: account) }
-  let(:contact_inbox) { create(:contact_inbox, contact: contact, inbox: twilio_inbox) }
+  let!(:contact) { create(:contact, account: account, phone_number: '+123456789') }
+  let(:contact_inbox) { create(:contact_inbox, contact: contact, inbox: twilio_inbox, source_id: '+123456789') }
+  let(:whatsapp_contact_inbox) { create(:contact_inbox, contact: contact, inbox: twilio_whatsapp_inbox, source_id: 'whatsapp:+123456789') }
   let(:conversation) { create(:conversation, contact: contact, inbox: twilio_inbox, contact_inbox: contact_inbox) }
+  let(:whatsapp_conversation) { create(:conversation, contact: contact, inbox: twilio_whatsapp_inbox, contact_inbox: whatsapp_contact_inbox) }
 
   before do
     allow(Twilio::REST::Client).to receive(:new).and_return(twilio_client)
@@ -71,7 +73,7 @@ describe Twilio::SendOnTwilioService do
       allow(message_record_double).to receive(:sid).and_return('1234')
 
       message = build(
-        :message, message_type: 'outgoing', inbox: twilio_whatsapp_inbox, account: account, conversation: conversation
+        :message, message_type: 'outgoing', inbox: twilio_whatsapp_inbox, account: account, conversation: whatsapp_conversation
       )
       attachment = message.attachments.new(account_id: message.account_id, file_type: :image)
       attachment.file.attach(io: Rails.root.join('spec/assets/avatar.png').open, filename: 'avatar.png', content_type: 'image/png')
diff --git a/spec/services/whatsapp/send_on_whatsapp_service_spec.rb b/spec/services/whatsapp/send_on_whatsapp_service_spec.rb
index 88f3f7740..deb7d6a3f 100644
--- a/spec/services/whatsapp/send_on_whatsapp_service_spec.rb
+++ b/spec/services/whatsapp/send_on_whatsapp_service_spec.rb
@@ -18,8 +18,9 @@ describe Whatsapp::SendOnWhatsappService do
     context 'when a valid message' do
       let(:whatsapp_request) { instance_double(HTTParty::Response) }
       let!(:whatsapp_channel) { create(:channel_whatsapp, sync_templates: false) }
-      let!(:contact_inbox) { create(:contact_inbox, inbox: whatsapp_channel.inbox, source_id: '123456789') }
-      let!(:conversation) { create(:conversation, contact_inbox: contact_inbox, inbox: whatsapp_channel.inbox) }
+      let!(:contact) { create(:contact, phone_number: '+123456789') }
+      let!(:contact_inbox) { create(:contact_inbox, contact: contact, inbox: whatsapp_channel.inbox, source_id: '123456789') }
+      let!(:conversation) { create(:conversation, contact: contact, contact_inbox: contact_inbox, inbox: whatsapp_channel.inbox) }
       let(:api_key) { 'test_key' }
       let(:headers) { { 'D360-API-KEY' => api_key, 'Content-Type' => 'application/json' } }
       let(:template_body) do
@@ -35,14 +36,12 @@ describe Whatsapp::SendOnWhatsappService do
         }
       end
 
-      let(:success_response) { { 'messages' => [{ 'id' => '123456789' }] }.to_json }
+      let(:success_response) { { 'messages' => [{ 'id' => 'message-123456789' }] }.to_json }
 
       it 'calls channel.send_message when with in 24 hour limit' do
         # to handle the case of 24 hour window limit.
-        create(:message, message_type: :incoming, content: 'test',
-                         conversation: conversation)
-        message = create(:message, message_type: :outgoing, content: 'test',
-                                   conversation: conversation)
+        create(:message, message_type: :incoming, content: 'test', conversation: conversation)
+        message = create(:message, message_type: :outgoing, content: 'test', conversation: conversation)
 
         stub_request(:post, 'https://waba.360dialog.io/v1/messages')
           .with(
@@ -52,7 +51,7 @@ describe Whatsapp::SendOnWhatsappService do
           .to_return(status: 200, body: success_response, headers: { 'content-type' => 'application/json' })
 
         described_class.new(message: message).perform
-        expect(message.reload.source_id).to eq('123456789')
+        expect(message.reload.source_id).to eq('message-123456789')
       end
 
       it 'calls channel.send_template when after 24 hour limit' do
@@ -66,7 +65,7 @@ describe Whatsapp::SendOnWhatsappService do
           ).to_return(status: 200, body: success_response, headers: { 'content-type' => 'application/json' })
 
         described_class.new(message: message).perform
-        expect(message.reload.source_id).to eq('123456789')
+        expect(message.reload.source_id).to eq('message-123456789')
       end
 
       it 'calls channel.send_template if template_params are present' do
@@ -79,7 +78,7 @@ describe Whatsapp::SendOnWhatsappService do
           ).to_return(status: 200, body: success_response, headers: { 'content-type' => 'application/json' })
 
         described_class.new(message: message).perform
-        expect(message.reload.source_id).to eq('123456789')
+        expect(message.reload.source_id).to eq('message-123456789')
       end
 
       it 'calls channel.send_template when template has regexp characters' do
@@ -106,7 +105,18 @@ describe Whatsapp::SendOnWhatsappService do
           ).to_return(status: 200, body: success_response, headers: { 'content-type' => 'application/json' })
 
         described_class.new(message: message).perform
-        expect(message.reload.source_id).to eq('123456789')
+        expect(message.reload.source_id).to eq('message-123456789')
+      end
+
+      context 'when source_id validation is required' do
+        let(:message) { create(:message, conversation: conversation, message_type: :outgoing) }
+
+        it 'marks message as failed when source_ids do not match' do
+          contact_inbox.update!(source_id: '1234567890')
+          described_class.new(message: message).perform
+          expect(message.reload.status).to eq('failed')
+          expect(message.external_error).to include('This conversation may have originally belonged to a different contact')
+        end
       end
     end
   end