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304 Not Modified

Your cached copy is still good. The reward for sending If-None-Match.

304Redirection
What it means
Your cached copy is still good. The reward for sending If-None-Match.
In practice
304 is not an error — it is caching working. The client sent If-None-Match (an ETag) or If-Modified-Since, and the server is saying “what you have is current, no body needed”. If you are debugging “why is my change not showing”, a 304 in the network tab means the browser asked and was told nothing changed: check what ETag the server computes, or hard-reload to bypass the conditional request.
Whose problem is it?
Nobody — the resource is elsewhere, and the client is being told where.