Storing Session on Dropbox / Deleting Images Does Not Work

I'm using Dropbox + Capture One as an alternative to the super slow UI of Lightroom CC.

Everything works as intended except the very necessary act of deleting old images.

It doesn't work at all. Delete. Command+Delete, nothing moves an image from a folder to the session trash.

Any idea why this is? Presumably it has to do with Dropbox's 'Confirm Deletion' feature.