Uploading file works on cloud but not local gateway

[Ploni_Almoni]

I'm using sandBlast api, when I upload to the cloud all is fine, but when I try to upload to local gateway I receive

code:1008,label:BAD_REQUEST, message: Invalid Multipart/form request

Why?

I'm not sending cookie to local gateway, I'm using CSharp.

I found the same issue here, but there is no answer yes, please If you can share a working code example for c# in local gateway.