Error on calling an API using Webclient - charset=UTF-8

I have a problem on calling an API using Webclient.In my request a see that Webclient automatically put this header:

Content-Type: multipart/form-data;boundary=--------------------------648852845839919888993842;charset=UTF-8

I always receive a response 404 Bad request because on the server side arrives the request without charset=UTF-8

Content-Type: multipart/form-data;boundary=--------------------------648852845839919888993842

I don't know which infrastructure component remove the charset=UTF-8 but if I do a postman request without charset=UTF-8 everything works fine.

So, the problem is, why Webclient automatically put this value on the Content-Type header?It’s possible to force Webclient to override it?