400 errors are usually about malformed requests. Double-check your JSON structure—it should be valid. Use a tool like [JSONLint](https://jsonlint.com/) to validate your JSON before sending it via curl.
Also, try escaping double quotes like this:
```bash
curl -X POST -H "Content-Type: application/json" -d "{\"key\":\"value\"}" https://example.com/api
```
Sometimes APIs are picky about how the JSON is formatted.
Also, try escaping double quotes like this:
```bash
curl -X POST -H "Content-Type: application/json" -d "{\"key\":\"value\"}" https://example.com/api
```
Sometimes APIs are picky about how the JSON is formatted.