I have built an integration that was refreshing tokens every 30 minutes for 2 months, then yesterday it stopped working. I get the same message: "response": {
"error_description": "Invalid client or client credentials",
"error": "invalid_client"
} In the code, I am setting the Authorization header: 'Authorization: Basic ' . base64_encode($request['api_key'] . ':' . $request['secret']) When I check the API key in the API Reference it works. Also, I have triple checked the API Key and Secret. I am able to complete steps 1-4 of the workflow: https://v3.developer.constantcontact.com/api_guide/server_flow.html But step 5 is breaking... not sure what could be wrong.
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