Thank you Alena, but that response is irrelevant to this issue. The Request Content Type has always been x-www-form-urlencoded... The API key has always been correct. Proxy still doesn't work unless you hard-code the API key into the Authorization field...
Please see my original post.
Stripe services do not work if you don't put "Bearer sk_ahsdyt985yethriudf" in the Authorization field. Using "Bearer {api_key_proxy}" does NOT work. The problem is with the setup of the proxy service...
Maybe in your response on the other thread you meant to address the other problem (testing the cardToken service from the Test tab in the builder). But that's a secondary problem (and it still doesn't work). I still don't know whether I should delete the stripe services and recreate them (and I'd have to redo all of the mapping for those services on all pages).. But this is the major issue (not being able to use the proxy service).