Troubleshooting Dust API Errors: mime_type Upsert Issues

Hi! 🙂 I'm totally stuck trying to use Dust API to upsert a table. I have an issue regarding mime_type field. I've the following error when I call the API :

[400] invalid_request_error Invalid request body: mimeType must not be provided.

However when I leave mime_type blank I have the following error :

[400] invalid_request_error Validation error: Required at "mime_type"

I've tried to test my request in Dust documentation but I keep having the same error... Someone could help me?