It seems like you're encountering a "404 resource not found" error when trying to add a contact to a workflow using the API. Double-check the correctness of the :workflowId and :email parameters in your API request URL, as well as the endpoint structure, to ensure they match the system's requirements. If the issue persists, you might want to consult the API documentation or reach out to the API provider's support for further assistance in resolving this specific error.