Hello user3132378,   Thank you for reaching out to Constant Contact API Developer Support. My team is here to assist outside software developers with questions about building into Constant Contact's API.   Thank you for providing the screenshot of the error report. It looks like we'll need some additional information in order to assist with troubleshooting. If you could please provide us with your API key, a full example authorization request, including headers, and any timestamps or general timeframes you may have for when this error has occurred, we'll be able to better assist in pinpointing the cause of the error. Please provide this information securely by reaching out to us via email at webservices@constantcontact.com, we look forward to assisting you!   Please let us know if you have any other questions!   Regards, ... View more