The resolution to this issue is often making sure you have entered a credit card or other valid method of payment even if you don't plan on needing to use it.
If there is an option to select "Review" or "Continue", select that and enter valid payment information if required. If there's problems doing this:
Tap: Settings > [your name at the top] > Media & Purchases > View Account > Review Apple ID.
More things to try in this 2018 post by Urquhart1244 marked Apple Recommended:
https://discussions.apple.com/thread/8434425?answerId=33542414022#33542414022
Payment methods that you can use with your Apple ID - https://support.apple.com/HT202631
If you still have problems:
Click here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service --> "See a list of Apple phone numbers around the world."
Click here --> https://support.apple.com/HT201232