page does not return to website after entering payment details

Hi,

I set the Return Page to My Accounts and set all the required info .
Paytm Staging server URL is https://pguat.paytm.com/oltp-web/processTransaction?orderid=%3COrder_ID.
After details of CC /DC or patm wallet is added, the page does not return to the website.
cannot see any success info. I see only a white page with the following written

Cannot POST /

How can I fix this?