@dean-houston from my tests it did look like the information was correctly retrieved from the purl, the distro of the uploaded package matched the distro from the purl and not from the specific query string parameter. I also used it for uploading other packages, but most of them have the metadata inside the package anyway.

Working:

http://localhost:8624/api/packages/my-debian/upload?purl=pkg%3Adeb%2Fnano%409.0-1%3Farch%3Di386%26distro%3Dwtf&distribution=x

Not working:

http://localhost:8624/api/packages/my-debian/upload?purl=pkg%3Adeb%2Fnano%409.0-1%3Farch%3Damd64%26distro%3Dwtf
Write-Error: Upload failed for pkg:deb/nano@9.0-1?arch=amd64&distro=wtf Distribution must be specified when adding a Debian package.

So the actual distribution doesn't matter since it's already part of the purl but upload fails when omitted.