I get two log entries when trying different configuations and attempting to Authorize the app from my website:
[23-Mar-2022 22:07:37 UTC] No valid access token found:
[23-Mar-2022 22:09:01 UTC] “Rakuten API Credentials” failed to exec curl: {“error”:”server_error”,”error_description”:”Error when issuing the access token”}
Maybe these will help. Thanks.