The sync with Quickbooks can sometimes get stuck or appear to be stuck. See below for more info depending on which version of Quickbooks you are using.
Technically, the sync never freezes for QB online, but it can take a while depending on what you are syncing. If you have invoices in the queue, then check for errors.
If there is nothing in the ready to sync queue and it has been over an hour then let us know. Otherwise, please wait about a half hour and get back to us.
If your sync has been running for more than an hour with no progress, then try force quitting the web connector application by right clicking the lime green folder icon in your toolbar.
If it does not respond, then it is frozen and will only return to normal when you restart your computer.
Afterwards, try syncing fewer invoices or none at all to better identify the problem