Webhook URL is Invalid

Hii Team,

          Currently we are trying to use webhook for getting back the signed document from adobe. But in the creation of webhook itself, we are getting an error that "webhook URL is invalid". We have tried becceptor with adobe for testing purpose. So it worked there . But when we tried with our production environment's webapi URL, we weren't able to create webhook.  We have provided the webapi URL as webhook URL in the format mentioned below,

[https://:[apiKey]@webapiurl]. 

But still we are getting that error message. Can anyone suggest how can we resolve this?

Thanks in advance.