# aiohttp.multipart.MultipartError: Could not find boundary in multipart body

- **ID:** `python/aiohttp-multipart-parse-error`
- **Domain:** python
- **Category:** data_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The multipart request body is malformed or missing the boundary parameter.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.7 | active | — | — |
| 3.8 | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   writer = aiohttp.MultipartWriter(); part = payload; writer.append(part); await session.post(url, data=writer)
   ```
2. **** (85% success)
   ```
   headers = {'Content-Type': 'multipart/form-data; boundary=myboundary'}; data = '--myboundary...'
   ```

## Dead Ends

- **** — If the server expects a specific boundary, it won't match. (70% fail)
- **** — The data cannot be parsed, leading to incomplete processing. (90% fail)