How do I set the scmToken when uploading files with the ReviewService.addFiles JSON API?

I'm successfully uploading the files from a git repo on the client to a review using the JSON API, with a snippet of the JSON being:

{"command": "ReviewService.addFiles", "args": {"reviewId": 28810, "zipName": "files.zip", "scmToken": "git", "changelists": ... and so on...

I've tried with both "GIT" (suggested by the quite poor documentation) and "git" but, whenever I query the review, the token comes back as 'none' and the files from git are lumped in to the same consolidatedChangelist as any other uploaded files.

Can anyone tell me what I am doing wrong?

S.