Comment by Imustaskforhelp

UPI in India if I remember correctly can actually work even offline by either sms/calling functionality even on dumb phones

Pasting this ddg-ai thing but I think its called UPI 123PAY

UPI 123PAY allows users to make digital payments using feature phones without needing a smartphone or internet connection. Users can set up a UPI ID by dialing *99# and can make payments through methods like IVR calls, missed calls, or sound-based technology.

https://razorpay.com/blog/what-is-upi-123-pay/