**Motivations:**
- Some NIP-95 endpoints require Accept and User-Agent headers
- Better diagnosis of HTML error responses (404, 403, 500)
- More detailed error messages for troubleshooting
**Root causes:**
- Missing Accept: application/json header may cause endpoints to return HTML
- Missing User-Agent header may cause some servers to reject requests
- HTML error pages need better detection and classification
**Correctifs:**
- Added Accept: application/json header to all requests
- Added User-Agent: zapwall.fr/1.0 header to all requests
- Improved HTML error detection with 404/403/500 classification
- Enhanced error messages with specific suggestions based on error type
- Increased body preview in logs from 200 to 500 characters for better diagnosis
**Evolutions:**
- None
**Pages affectées:**
- pages/api/nip95-upload.ts