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Is there anyone who can help me in using Access_token in my PHP Web Application.

right now i am stuck on access_token and i want to test my Fax function but Using PHP SDK i am stuck on Refresh_token function it is giving error and looks like my SDK is not using Access_token....

i am getting this error

authData.php Auth exception: Refresh token has expired Exception: Unauthorized for this grant type SDK HTTP Error at https://platform.devtest.ringcentral.com/restapi/oauth/token Response text: { "error" : "unauthorized_client", "error_description" : "Unauthorized for this grant type", "errors" : [ { "errorCode" : "OAU-251", "message" : "Unauthorized for this grant type" } ] }