406 Not Acceptable
Last reviewed: 2026-04-22
HTTP 406 Not Acceptable usually means the server could not produce a response matching the request’s Accept headers or content expectations.
Quick answer: The request reached the server, but the server could not return a response in an acceptable format.
What this error means
The request reached the server, but the server could not return a response in an acceptable format.
When this error usually appears
- Using APIs
- Sending specialized Accept headers
- Requesting content in unsupported formats
Common causes
- Accept-header mismatch
- Unsupported response format
- Application content-negotiation issue
How to fix it
Start with the least disruptive fixes first, then move into deeper troubleshooting only if the issue continues.
Retry with a simpler request if possible
Reducing strict format expectations can help confirm a negotiation problem.
Check whether the issue affects only one endpoint
That helps identify a content-negotiation problem on a specific resource.
If you run the service, inspect content-negotiation logic
406 errors often point to response-format compatibility issues.
Frequently asked questions
Is 406 mainly about content negotiation?
Yes. It usually means the server could not satisfy the requested acceptable response format.