Recently we have seen an increased number of status code 406 returned from the testcases on our Zendesk integration. The error occurs on roughly 10% of the API calls. Since we have not changed any code, this seems to be caused by a change on the Zendesk end. In plain HTTP 406 is used to signal that a valid response could not be generated based on the "Accept" header. The header is set to "application/json", but the 406 still occurs.
How can we figure out what is causing the 406 errors?