If-Match required

What it means

A write arrived without an If-Match header. It is required rather than optional, because optional optimistic concurrency is absent optimistic concurrency: the client that omits it is precisely the one that silently overwrites a colleague's edit.

What to do

Read the record, take the ETag from the response, and send it back as If-Match on the write.

The response

{
  "type": "https://casanova.realty/problems/precondition-required",
  "title": "If-Match required",
  "status": 428,
  "detail": "A sentence about this particular occurrence.",
  "instance": "/api/v1/properties/some-listing"
}

Content type is application/problem+json. Match on type, not on title — the title is prose and may be rewritten.