400 Bad Request · type invalid_request
When it happens
The request body is larger than 2 MB, judged by its Content-Length header or by what actually arrived. A quote with 25 policies and every field at its longest is about 1.3 MB, so a real request shouldn’t come close.
What to do
Check that you aren’t sending something you didn’t mean to, such as an encoded document. Don’t retry the same request.
Example
400 Bad Request