#### Problem
Meta requires the app to be subscribed to the WABA before
`override_callback_uri` can be used. The current implementation tries to
use `override_callback_uri` directly, which fails with:
> Error 100: "Before override the current callback uri, your app must be
subscribed to receive messages for WhatsApp Business Account"
This causes embedded signup to fail silently, the inbox appears
connected but never receives messages.
#### Solution
Split `subscribe_waba_webhook` into two sequential API calls:
```ruby
def subscribe_waba_webhook(waba_id, callback_url, verify_token)
# Step 1: Subscribe app to WABA first (required before override)
subscribe_app_to_waba(waba_id)
# Step 2: Override callback URL for this specific WABA
override_waba_callback(waba_id, callback_url, verify_token)
end
```
#### References
- Subscribe app to WABA's webhooks: https://www.postman.com/meta/whatsapp-business-platform/request/ju40fld/subscribe-app-to-waba-s-webhooks
- Override Callback URL (Embedded Signup): https://www.postman.com/meta/whatsapp-business-platform/request/l6a09ow/override-callback-url
Co-authored-by: Sojan Jose <sojan@pepalo.com>
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