The Plugin is from Paytm itself, from [login to view URL]
So a plugin does not need to be built from scratch.
The plugin works as expected in Staging (Testing mode) with test credentials, with one problem. Automatic Email order Notifications with pdf invoice are sent Vendor, but not to Shopper. Testing with other Virtuemart Payment Plugin, VM Standard, produced positive results - both vendor and shopper were automatically sent order emails with pdf invoice.
I need someone to have a look at the code and correct it for me. You should be familiar with Virtuemart and joomla programming language.