AmEx is quite funny when it comes to earning points.
In the german pdf version of their t&c for Platinum cards, which is 62pages long btw, they state they can chose to stop issueing points for any transaction at any time.
AFAIK they only applied this rule when making PayPal Germany payments to other users via “sending money to friends” which is free and which allows paying by AmEx.
Reason for this is that AmEx says sending money, or “uploading” money to any service is considered not a purchase but rather a money transfer which is not points earning.
So keep that in mind that AmEx can decide at any point to not offer points / MR for any transaction whatsoever and unfortunately there is nothing the merchant can do about it to change AmEx decision nor can the AmEx user do anything.