I can’t add or update my payment details

Check the following

1. The payment method that you are adding is of the same country as that of App Store Country on your iPhone
2. You have valid payment plan / debit / credit card from an authorised bank from the same country
3. Payment methods that you can use with your Apple ID - Apple Support

If you can't choose None when you edit your Apple ID payment information

1. If you have an unpaid balance or payment due
2. If you have a subscription that automatically renews
3. If you're using the iTunes Store or App Store for the first time
4. If you are not in the country or region you’re creating an Apple ID for
5. If you changed your country or region
6. If you're a part of Family Sharing

Thank you. I however, complied to everything listed above. I’m not even trying to choose none. I’m trying to add a Barter Card because a lot of the banks that issue cards in this country have issues with the currency conversion process. I’ve been trying to add the card all day but it keeps telling me the iTunes store is unable to process purchases at this time. I'm not even trying to buy anything...yet. I just want to add the card in advance.