Hi Jennifer, Thank you for getting back to me. I tested with both REST Api apps, "ONE Simple Plan" and "Default Application" under my sandbox business account, I still got the same error as I got on Monday. My sandbox merchant ID (account ID) is : TRL57SX523SWL as I already sent you. I used the "client ID" and "secret" of the app to obtain an access token, then I use the access token to create an order as a first step to initiate future transaction. it works. Then for the second step "authorize payment", I used the order id and one of the previous transaction ids of the payment to this sandbox business account, there was the same error (permission). Am I missing anything? Kind Regards, Wen
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