The “Your FTP quota has been exceeded” error is a specific error from MonstaFTP. It seems to happen randomly and it’s not clear to us why it happens sometimes for some people on some actions. But it doesn’t seem to have anything to do with what you’re uploading or what’s already on your account.
We should fix this issue but haven’t been able to do so yet. In the mean time, you may want to skip the online file manager and use a desktop FTP client like FileZilla instead.
I know filemanager.ai loves throwing Your FTP account quota has been exceeded even when you are well below any limits, that’s why I use FileZilla instead.