Learn how you can set a webhook/callback URL for your app.
For instance, if we generate a URL on webhook.site and set that URL as the callback URL for our WhatsApp Access API app on Gupshup, we will receive the following event.
You can use such tools to understand what payload Gupshup sends to your callback URL that you need to accept and handle in your web service.
Once your web service is scripted and deployed - use tools like Postman to test it by sending a dummy payload similar to what you receive while trying with webhook.site URLs. If your web service meets all the criteria mentioned here, you will successfully set the callback URL in the WhatsApp app.
Please try this approach to resolve your issue. If the problem persists, you can reach out to us at firstname.lastname@example.org