[mothered]

Given I'm located far away from the person in question, I have logged into his account on
- a fresh device
- via VPN server located in the same city that he is in

There's a possibility that Amazon may believe the account has been compromised, hence they're not allowing transactions to go through.

What was also weird was that when I entered live chat on amazon (to ask why the payment is getting declined) the representative asked „am I talking to [name of acc owner]?“

For security reasons, they need to be certain they're speaking with the rightful owner.

How did you respond to their question?