4xx Client ErrorCommonly usedRFC 9110
415Unsupported Media Type
Content-Type is not supported by the server.
What it means
The server refuses to accept the request because the payload format (Content-Type) is not supported. For example, the server expects application/json but the client sent text/plain.
When to use it
- ✓Client sent wrong Content-Type
- ✓Server only accepts JSON but received form data
Common causes
- →Missing Content-Type: application/json header
- →Sending form data to a JSON-only endpoint
- →Uploading wrong file format
Code Examples
Fix: set correct Content-Type
javascript
// Wrong — missing Content-Type
fetch('/api/users', { method: 'POST', body: JSON.stringify(data) });
// Correct
fetch('/api/users', {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify(data),
});Don't confuse with
Quick Facts
Code415
CategoryClient Error
SpecRFC 9110
CommonYes
Relevant Headers
Content-Type
Must match a type the server accepts