Currently, I don't think any PSP app is giving option to pay to other app QR over UPI from their wallet. Basically, the interoperability use case.
For example, if you scan a Paytm QR code, from Paytm app - it gives option to pay by Paytm wallet, linked UPI bank accounts.
But, if you scan any other UPI QR code, Paytm app just gives option to pay from linked bank accounts and will not give option to pay from Paytm wallet.
Paytm being main player in UPI and wallet environments, I don't think there are many transactions that happen in this use case.
Currently, I don't think any PSP app is giving option to pay to other app QR over UPI from their wallet. Basically, the interoperability use case.
For example, if you scan a Paytm QR code, from Paytm app - it gives option to pay by Paytm wallet, linked UPI bank accounts.
But, if you scan any other UPI QR code, Paytm app just gives option to pay from linked bank accounts and will not give option to pay from Paytm wallet.
Paytm being main player in UPI and wallet environments, I don't think there are many transactions that happen in this use case.