Hi Pankaj,
We have installed Guru 5.1.7 on the staging server and the Stripe plugin 1.0.4 as well. The server is running with Joomla 3.9.3 and PHP 7.2.16.
It has the same behavior. We apply the discount code and it is asking for the last name and other payments information. (same as earlier version). Why is it doing the test before getting the result from the discount code?
You have super user access to the server. Let us know when done.
Please let us know how you fix it as we have to replicate the modifications on the production server.