'Missing minidump upload' when uploading a minidump

I have set up version 9 for the on-premise Sentry and I’m trying to get the minidump functionality working.

When I do a POST call to the minidump API with a dump the actual files seems to be dropped somewhere along the line and I just get a ‘Missing minidump upload’ message. I tried adding a print on the request.FILES and it’s empty. When I do the same API call to sentry.io with the same file everything works as intended.

Any ideas of where or why the actual files is dropped? I can see the request logged in Sentry but just without the actual file.