This error message indicates that you are using an HTTP method other than POST, such as GET. In order to avoid this error message, you will need to use the POST method. To determine which HTTP methods are supported for a specific API method, you can visit the documentation for that method at open.convio.com.

If you are already using POST and still receiving that error message, check to see if your organization has a custom secure domain configured. Redirects to custom secure domains are done via an HTTP 301 status, which transforms all requests to a GET method regardless of the original method. In this scenario, you will need to post your API requests to your organization's custom secure domain to avoid the redirect.