The request is understood but cannot be applied to the current resource state.
Likely causes
- Newer concurrent version
- Object already exists
- Incompatible business state
- ETag or application lock
Checks in priority order
- Read the error response body
- Fetch the current resource
- Compare version or ETag
- Retry with correct preconditions
When to escalate
Escalate when the failure affects multiple users, a production dependency is unavailable, or logs show a component outside your control. Include timestamps, scope, tests already performed, and the last known working state.