fix: Subscribe app to WABA before overriding webhook callback URL (#13279)

#### 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>

app/services/whatsapp/facebook_api_client.rb

@@ -61,6 +61,25 @@ class Whatsapp::FacebookApiClient
   end
 
   def subscribe_waba_webhook(waba_id, callback_url, verify_token)
+    # Step 1: Subscribe app to WABA first (required before override)
+    # Meta requires the app to be subscribed before using override_callback_uri
+    # See: https://github.com/chatwoot/chatwoot/issues/13097
+    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
+
+  def subscribe_app_to_waba(waba_id)
+    response = HTTParty.post(
+      "#{BASE_URI}/#{@api_version}/#{waba_id}/subscribed_apps",
+      headers: request_headers
+    )
+
+    handle_response(response, 'App subscription to WABA failed')
+  end
+
+  def override_waba_callback(waba_id, callback_url, verify_token)
     response = HTTParty.post(
       "#{BASE_URI}/#{@api_version}/#{waba_id}/subscribed_apps",
       headers: request_headers,
@@ -71,7 +90,7 @@ class Whatsapp::FacebookApiClient
       }.to_json
     )
 
-    handle_response(response, 'Webhook subscription failed')
+    handle_response(response, 'Webhook callback override failed')
   end
 
   def unsubscribe_waba_webhook(waba_id)

spec/services/whatsapp/facebook_api_client_spec.rb

@@ -161,6 +161,18 @@ describe Whatsapp::FacebookApiClient do
 
     context 'when successful' do
       before do
+        # Step 1: Subscribe app to WABA (no body)
+        stub_request(:post, "https://graph.facebook.com/#{api_version}/#{waba_id}/subscribed_apps")
+          .with(
+            headers: { 'Authorization' => "Bearer #{access_token}", 'Content-Type' => 'application/json' }
+          )
+          .to_return(
+            status: 200,
+            body: { success: true }.to_json,
+            headers: { 'Content-Type' => 'application/json' }
+          )
+
+        # Step 2: Override callback URL (with body)
         stub_request(:post, "https://graph.facebook.com/#{api_version}/#{waba_id}/subscribed_apps")
           .with(
             headers: { 'Authorization' => "Bearer #{access_token}", 'Content-Type' => 'application/json' },
@@ -180,19 +192,45 @@ describe Whatsapp::FacebookApiClient do
       end
     end
 
-    context 'when failed' do
+    context 'when app subscription fails' do
       before do
+        stub_request(:post, "https://graph.facebook.com/#{api_version}/#{waba_id}/subscribed_apps")
+          .with(
+            headers: { 'Authorization' => "Bearer #{access_token}", 'Content-Type' => 'application/json' }
+          )
+          .to_return(status: 400, body: { error: 'App subscription to WABA failed' }.to_json)
+      end
+
+      it 'raises an error' do
+        expect { api_client.subscribe_waba_webhook(waba_id, callback_url, verify_token) }.to raise_error(/App subscription to WABA failed/)
+      end
+    end
+
+    context 'when callback override fails' do
+      before do
+        # Step 1 succeeds
+        stub_request(:post, "https://graph.facebook.com/#{api_version}/#{waba_id}/subscribed_apps")
+          .with(
+            headers: { 'Authorization' => "Bearer #{access_token}", 'Content-Type' => 'application/json' }
+          )
+          .to_return(
+            status: 200,
+            body: { success: true }.to_json,
+            headers: { 'Content-Type' => 'application/json' }
+          )
+
+        # Step 2 fails
         stub_request(:post, "https://graph.facebook.com/#{api_version}/#{waba_id}/subscribed_apps")
           .with(
             headers: { 'Authorization' => "Bearer #{access_token}", 'Content-Type' => 'application/json' },
             body: { override_callback_uri: callback_url, verify_token: verify_token,
                     subscribed_fields: %w[messages smb_message_echoes] }.to_json
           )
-          .to_return(status: 400, body: { error: 'Webhook subscription failed' }.to_json)
+          .to_return(status: 400, body: { error: 'Webhook callback override failed' }.to_json)
       end
 
       it 'raises an error' do
-        expect { api_client.subscribe_waba_webhook(waba_id, callback_url, verify_token) }.to raise_error(/Webhook subscription failed/)
+        expect { api_client.subscribe_waba_webhook(waba_id, callback_url, verify_token) }.to raise_error(/Webhook callback override failed/)
       end
     end
   end