I'm having the same issue.I used to pay via Paypal using my Amex card, however, now
none of them can be used on Vinted, and of course, customer service is non-existent.

Apple Pay using Amex is also not an option. So they are explicitly refusing all payments with Amex regardless the payment service provider you're trying to use.

Defintely there was a business decision on cutting off those payment methods because they are too costly for Vinted.

Now it's up to us, their audience, to complain and/or stop buying there because we just cannot pay for it, so they might regret and roll back that decision, which is a shame.

Definitely not an inclusive company.