406 Not Acceptable — Causes & Fix
HTTP 406 (Not Acceptable) means the server can't produce a response matching the formats the client said it would accept (via the Accept headers).
- Applies to
- Any website or web server (HTTP standard)
- Time to fix
- 5–30 minutes
What it means
Causes include an Accept header requesting a content type the server can't provide, or overly strict content negotiation. HTTP status 406 is defined in RFC 9110 (HTTP Semantics). This is a client-side (4xx) error — the request itself had a problem, so the fix is usually on the requester's side or in how the server validates the request.
Symptoms
- "406 Not Acceptable" from an API
- A client requesting a specific format gets rejected
How to fix it
- 1
Adjust the Accept header
1. Request a format the server supports (e.g. application/json).
- 2
Relax negotiation (developers)
1. Ensure the server offers a sensible default when the requested type isn't available.
Frequently asked questions
What causes a 406?
Usually the client's Accept header asks for a media type the server can't return. Align the requested type with what the API produces.
Last updated July 20, 2026
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