Upi id invalid

It is depending on what type of iPhone / which iOS you use.

According to a recent NPCI mandate for banks (in your country), UPI is not available for iOS versions <13.4

You can contact your bank to verify.

Using a gift card may offer a solution to add money to Apple Store, if your UPI ID remain invalid.

See this Apple article: What type of gift card do I have?

https://support.apple.com/en-gb/HT204199