Here are details that have derailed previous enrollments, per some earlier problem reports posted around here:
As mentioned above, you’ll need to associate a major payment card with the Apple ID, and not an Apple ID balance. No gift cards.
Some of the other usual suspects:
If you have an add-on VPN client app in use, discontinue and remove that.
If you’re using the developer website to enroll, try enrolling via the developer app. Or vice versa.
If you’re in India and using (trying) the website, you’ll need to use the developer app to enroll. (AFAIK, Nepal can use both. Or can try both.)
If you have a mobile number format Apple ID, those usually haven’t worked and an email-format was (is?) needed.
If you’re in an embargoed or restricted region or country, that enrollment won’t work. Nepal, AFAIK isn’t.
If you’re a denied person, that enrollment won’t work.
If you’re in a country or region where Apple isn’t active, that probably won’t work.
If you can’t be reached via direct incoming international call, find a communications carrier that allows that.
Apple Gift Card and Apple ID balances won’t work for enrollments.
If one of those is not the case here…
Contact Apple Developer Support.
