It's literally telling you how to 1) debug the problem and 2) provide the information that will let us help you debug it further. If you don't want help from us, don't post here.
@Junhua-liu: And posting a 1-star review in the App Store and then refusing to provide any information that would let us actually help you solve the problem is really not appreciated.
In any case, looking at your account, there's no mystery here — you're just at your file storage quota, so additional files were never uploaded. The page I linked to explains this clearly as a possibility, and it also explains where to see the error you're getting on every sync telling you you're at your quota.
We'd appreciate if you would update your review. Zotero is working correctly. You're just at your quota and ignored the warning Zotero was showing you.
What is wrong with you? You left a public 1-star review of our app claiming it didn't work and then refused to read our documentation or provide any information here that would let us help you, all because you ignored a warning in the desktop app. And after I explained what the problem is, this is still your response? Why are you treating people trying to help you this way?
Upgrade Storage
In any case, looking at your account, there's no mystery here — you're just at your file storage quota, so additional files were never uploaded. The page I linked to explains this clearly as a possibility, and it also explains where to see the error you're getting on every sync telling you you're at your quota.
We'd appreciate if you would update your review. Zotero is working correctly. You're just at your quota and ignored the warning Zotero was showing you.