Payfast ITN gives me the following error: "The response contained an invalid header"

Hi I added my itn (notify_url) route to VerifyCsrfToken's except array, followed the documents but the itn or notify_url keeps giving me the error - "The response contained an invalid header" when I view it in https://sandbox.payfast.co.za/ ITN hits. I can't seem to find where the curl options and headers have been set to see it all is correct? Could you advise please?