I always get:
Missing end boundary in multipart body.
API Sandbox doesn't help. It is possible to create folder there.
The request is: curl https://www.googleapis.com/upload/drive/v3/files?uploadType=multipart -d @/home/payload -H 'Authorization: Bearer mytoken' -H 'Content-Type: multipart/boundary; boundary=RubyApiClientUpload'
The payload is:
--RubyApiClientUpload
Content-Type: application/json
{ "mimeType":"application/vnd.google-apps.folder", "name":"newfolder", "parents":["0AMtAREF....."] }
--RubyApiClientUpload
--RubyApiClientUpload--