Hi. Thanks for this. Unfortunately:
1. I am not doing an App Store or Itunes puchase
2. my payment method is not declined
That said, I called Apple support and they confirmed that some specific travel cards indeed are only compatible with some specific payment methods and/or with an iCloud account from one or more specific locations.
Trying to add one of these transit cards when one of the requirements is not met (payment method location and/or icloud account location) results in the following message:
Payment Method Required
Add a debit or credit card to Wallet and then try again.
The solution is to switch your iCloud account to the same country as that of the transit card. Beware that you might lose access to some Apple services (eg, Apple Music) if they are not available in the new location. Also, most chances are that your existing payment methods will be invalidated (but not always the case) and you might need to enter a new, local one. Again, different rules may apply based on origin x destination combination, so probably not worth playing with fire unless you are spending a lot of time in the place.