We are trying to implement the reauthentication flow.

I am attempting to use the Refresh Token Flow documented here - https://developer.ringcentral.com/api-docs/latest/index.html#!#RefRefreshTokenFlow

I am hitting the following endpoint to refresh my access token - POST /restapi/oauth/token HTTP/1.1

My headers are the following - headers={"User-Agent"=>"Faraday v0.9.2", "Content-Type"=>"application/x-www-form-urlencoded", "Authorization"=>"Basic {{API_KEYS_HIDDEN_FOR_SECURITY_CONCERNS}}", "Application"=>"application/json"}

My body is the following -body={:client_id=>"{{CLIENT_ID_HIDDEN_FOR_SECURITY_CONCERNS}}", :client_secret=>"{{CLIENT_SECRET_HIDDEN_FOR_SECURITY_CONCERNS}}", :grant_type=>"refresh_token", :refresh_token=>"{{REFRESH_TOKEN_HIDDEN_FOR_SECURITY_CONCERNS}}"}

However when I make a request I receive the following error -

API Error: invalid_client: Invalid client: { "error" : "invalid_client", "errors" : [ { "errorCode" : "OAU-153", "message" : "Invalid client: ", "parameters" : [ { "parameterName" : "client_id", "parameterValue" : "" } ] } ], "error_description" : "Invalid client: "}

Can you please advise as to what the error code "OAU-153" means and what the issue might be? The client_id is not blank, and the headers appear to be correct per the documentation linked to above.