Senior N8n Expert for Vonage Api Integration and Workflow Troubleshooting

We are seeking a highly skilled and experienced Senior n8n Expert for a long-term collaboration focused on designing, implementing, and maintaining complex automation workflows. A critical requirement for this role is proven expertise in integrating with the Vonage api to manage communication solutions, including sms, voice, and video functionalities. For our initial project, we require a specialist to troubleshoot a specific issue with an existing n8n workflow integrated with Vonage.

Current Context:

Our Vonage account is active with balance and a Spanish landline number, correctly linked to the application Item_Middleware_Comms inside Vonage. The n8n workflow consists of four nodes:

1. Webhook (voice-in) – listens for incoming Vonage calls.
2. Code – returns a json object (ncco) for vonage to speak a message.
3. Respond to Webhook – sends the NCCO response back to Vonage.
4. Send to Middleware – an optional step to forward data.

Current Situation / Problem:

The workflow executes successfully in n8n with no connection errors. Vonage Voice Logs show inbound calls, but all end as "Failed – Callee currently unavailable". In browser tests, the webhook returns the ncco json correctly. However, when making a real phone call, it does not work successfully.

Goal for the Specialist:

1. Diagnose why Vonage isn't recognizing the ncco response from n8n, likely related to json structure or response headers.
2. Validate that the webhook properly handles Vonage’s get/post request pattern.
3. Ensure the call plays back the spoken message successfully.

This initial task is expected to take no more than two hours for an expert.