Issue with callback from the paytm payment gateway.

[roshankrm]

Everything works perfectly after deploying on heroku but the payment gateway doesn't work. It says the syntax of callback url is not correct. In the server.js file, the callback url is specified as - paytmParams['CALLBACK_URL'] = 'callback';
I have attached the screenshot of the problem.

I also tried specifying the callback url as '/callback', '' '/callback', 'https://securegw-stage.paytm.in/callback'. None of them worked.

The heroku logs do not show any error either, it is also attached