Most likely cause: iPad not connected or needs a refresh / delete and reinstall.
Below is a list of quick fixes to try. Please work your way through them, and test after each one to see if the issue is solved;
Are you cashing up all iPads every day? If you are not cashing up on any of them, this can cause syncing issues. Try a cash up on all iPads (leaving them locked at the pin pad screen until all are cashed up) then reopen them once all are done. Give them a couple of minutes to clean up properly and test again.
Are all of your iPads running the correct Apple operating system (iOS) to be using posBoss? Check out this article. If you have an older iPad in the mix, you may need to consider retiring it and purchasing a newer one.
Try closing & reopening the posBoss App on all iPads then give the iPads a reboot.
Check your Wi-Fi is correct and working: (are iPads connected to the correct wi-fi? / iPads can connect to a news site on the internet? And are in range of the router?
Check storage on the iPad (Settings > General > Storage...) - if you have less than 25% storage available, delete something to recover space.
Reboot your router (Turn router off at power source for 1-2 minutes. Switch back on and allow 2 minutes to reconnect).
If you have tried all of the above and you're still experiencing issues please let us know, but there may be a wider issue with your internet provider.
If so, you will need to select one till to work with until the issue is resolved. (Tip: Check all tabs before payment for missing items that may not have synced through).