Unable to add my debit card details on Apple Account for payment

Re: "I’m trying to pay for an app and also iCloud+ .... experiencing difficulties in uploading my debit card details"

If needed: Find out how to pay an unpaid order.

If a message says 'billing problem with previous purchase' or 'verification required' - Apple Support

Else: To check which payment methods Apple can accept in your country or region:

See: Payment methods that you can use with your Apple Account - Apple Support

Wondering where you were trying to upload the card details.

See how to: Add a payment method to your Apple Account - Apple Support

or

you can : Log-in to your account online to update details or make changes: https://account.apple.com/

If needed: Apple Account Support website (info. / support / contsact options etc.) :

Apple Account - Official Apple Support