What does HTTP 412 mean?
A precondition in the request headers evaluated to false.
Common causes and when you see it
If-Match or If-Unmodified-Since checks failed.
How to fix or handle it
Reload the resource to get a fresh ETag and retry.
Test it yourself
Send a request with the online API tester, inspect the response with the HTTP header checker, or host an endpoint that returns 412 with the mock API generator to see how your app reacts.
HTTP 412 questions
A precondition in the request headers evaluated to false.
If-Match or If-Unmodified-Since checks failed.
Reload the resource to get a fresh ETag and retry.