Your merchant app, after you confirm your order, when initiated for payment, displays the mode of payment available for that particular product. For example, if you have installed Google Pay, Phone Pe, Samsung Pay, Apple Pay, etc. while making payment, logos of these mobile wallet apps display on the payment page. You can then figure out your method of payment and proceed to complete the transaction. In case your merchant app does not display the e-wallet app that you have, then you can choose to pay with debit or credit card and wait until it gets integrated with the merchant app.