Saving Talk file attachments to WebDav external storage. File not being written?

I’ve set up an external storage for a user on Nextcloud. This external storage is connected via WebDav. The external storage shows and performs as expected within the Files app - as in I can add/delete/copy/rename in Files and that is mirrored correctly on the actual server where the files are stored remotely.

When using this exact same connected WebDav folder in Talk - setting Talk to use that destination for saving incoming file attachments, things get a bit odd…

The file attachment/file is received in Talk, looking in Files the file has been placed in the correct location. However, looking on the actual server - no file is there. Not only is no file viewable, there’s no space being taken up either, and no hidden file. Yet the Files app says it’s located there and is, in my view, fetching it from there.

Is this a permissions issue? Is Talk writing the file to the remote server with permissions that only allow NextCloud apps to see its presence?

EDIT: So I’ve done a little more investigating and the more it’s pointing to a permissions issue. If I use Files to create a copy of the file in the same location, the copied file shows up on the remote server. The original still does not. The only difference I can see here is the permissions for the original file are owned by the sender, but the permissions of the copied file are owned by me. But I still can’t fathom a way round this problem, or indeed if there even would be a way round.

Second EDIT: If I initiate the WebDav service in reverse, things work. So If I connect my remote server to folder on NextCloud where files are being store for the purpose of Talk attachments, then all files are synced. The key word being synced. As opposed to stored solely on the remote server as described in my original idea. No permission issues. Syncing was never my idea, though, as I don’t really want them on my NextCloud server at all, mainly due to storage limits. I have NextCloud running on a hosted webserver and my file storage on a server at home, with a lot of space. It would also require me/the remote server to know the NextCloud users password. The other way round would not, it would only require the user to set up the storage on their NextCloud account - and it’s fine, they already know the remote sever login credentials.

Any pointers on what is going on here would be greatly appreciated. I know this may sound like an unusual use case, but for me, it could serve a great purpose.