As part of our plans for stricter validation in our REST API, we introduced a preview header to test out the changes before the rollout. Stricter validation has been postponed and beginning January 31, 2019, we will no longer support this header:
We still believe that stricter validation would have a positive impact on our REST API overall and are looking for alternative ways to introduce it. Stay tuned for future updates.
If you have any questions, please reach out!