I've upgraded my Zotero storage, but am still unsure what gets priority to sync with the cloud. I'm eager to use the iOS app to annotate pdfs, and it seems like some recent-ish additions to my library have shown up there fine, but then I get "unable to display document" when I try to open another pdf I just looked at through Zotero on my laptop. When I sync, I get the message "You have reached your Zotero File Storage quota. Some files were not uploaded. Other Zotero data will continue to sync to the server" with the pdf I'm trying to sync to the cloud named as the file not uploaded. But I know there are things being synced I don't need access to right now; can I make those go away?

I've tried to change sync attachment files to My Library to download "as needed" and closed, re-opened both desktop and ipad app. I've also deleted the attachments and reattached, created new item and tried again. And still I cannot open this one pdf I really need and added to my library just this week, though others I added to my Zotero library last year seem to open and download on the ipad just fine. I've looked through the documentation to see if anyone else had this problem and couldn't find an answer. The iOS keeps saying this pdf is either not a PDF file or might be corrupted, but I can open it other places fine. So I'm not sure if it's this particular PDF or what. Other files look like they are syncing but then don't seem to actually be on the iOS, further confusing me about what files are uploaded or not.

Questions:
-Is there a way to change what files get priority when syncing with Zotero storage? If so, how do I do that?
-Can I delete what files are being synced and start afresh without ruining my local Zotero storage?
–What is the best way to get the files I need to download on the ipad so I can just use Zotero storage to move things back and forth?