When there's a call to the revoke endpoint with an invalid/non-existent or expired token, it returns a 200 response as if it had successfully deleted the token. The expectation, in this case, is that a 400 status would be returned.
All supported versions of the API Gateway
All supported versions of the OTK
https://tools.ietf.org/html/rfc7009#section-2.2
The authorization server responds with HTTP status code 200 if the token has been revoked successfully or if the client submitted an invalid token.
Note: invalid tokens do not cause an error response since the client cannot handle such an error in a reasonable way. Moreover, the purpose of the revocation request, invalidating the particular token, is already achieved.
The content of the response body is ignored by the client as all necessary information is conveyed in the response code.