[Membership 2 Pro] REST API of membership plugin stopped working

I’ve been working with your REST API since January. Through the API I was able to give specific members access to our shop on https://therapeuten.tfmshop.de .

I’ve been using the following route: https://therapeuten.tfmshop.de/wp-json/membership2/v1/member/subscription?pass_key=8UIwUQlnc8.
It worked fine, but suddenly Wordpress doesn’t find the right route to go… Here’s what the browser shows:

{"code":"rest_no_route","message“:“Couldn’t find a route which has the same URL and request method","data":{"status":404}} (translated from German)

I don’t know where to start - the request/code didn’t change since quite a long time. Was there an update and something went wrong?