How can i add payment details

Start here:--> Change, add, or remove Apple ID payment methods - Apple Support

if the issue persists, contact iTunes Store Support Team, using this link:--> iTunes Store & App Store – Get support for various issues

choosing: your country, then Apple ID, then iTunes & App Store. If your problem is not among the options shown there, tap/click on the option “the topic is not listed” and describe your issue.

Regards

Giulio