A 428 Precondition Required error is a webserver’s code for: "The server requires conditional headers to prevent you from accidentally overwriting someone else's work.".

How do I fix or troubleshoot a 428 Error?

Common steps include reloading the page in your browser, checking for typos in the URL, verifying server status, clearing browser cache or cookies, and contacting the website owner or server administrator if the error persists.

428 Error | Error-Message.Net

A 428 Precondition Required error indicates that the origin server requires the request to be conditional.

Its primary purpose is to prevent the “lost update” problem, where Client A fetches a resource, Client B fetches the same resource, Client B updates it, and then Client A inadvertently overwrites Client B’s changes because neither request was conditional.

Determining why

The server’s API rules state that any modification (PUT, PATCH, DELETE) must include conditional headers such as If-Match with the current ETag. Because your request omitted the required precondition header, the server safely rejected it.

Steps you could possibly take:

Fetch the latest resource state - Perform a GET request to obtain the current version and its ETag response header.
Include the precondition header - Re-send your modification request including If-Match: "<etag>" or If-Unmodified-Since.

Source: RFC 6585 Section 3 (Additional HTTP Status Codes)