So the url provided by external company looks like:
https://company.sharepoint.com/sites/AAAA/Shared Documents/Forms/AllItems.aspx?ga=1&id=/sites/AAAA/Shared Documents/BBBB/CCCC/DDDD

I can manually (using the same account) upload files to CCCC and DDDD folders, don’t have any permission above this level.

And it always fails with “Unauthorized” error. I cannot select the path as I don’t have access to their entire sharepoint so rely on pasting the paths as custom values as below:
(I also tried Site Adress: https://company.sharepoint.com/AAAA and the same error)

Any idea if this is possible to get around? I can’t get any more SharePoint permissions sadly.