RedirectURL of payment gateway

I created a new payment plugin for phonepe payment gateway. Its working fine but i dont know what should be the returnURL once the payment is made.
I tried.
1.   var tempQueryParameters = queryParameters.Where(parameter =>
            !string.IsNullOrEmpty(parameter.Value))
            .ToDictionary(parameter => parameter.Key, parameter => parameter.Value);
            var returnURL = tempQueryParameters["return"];

2. http://localhost:15536/onepagecheckout#opc-confirm_order

You can follow other payment plugin that provided by default nopCommerce.

Like PayPal Commerce (the official integration)