This issue has been fixed with the latest version of the Check-Ins app; Version: 1.22 (76)
There is a known issue with our latest Check-Ins Station app on iOS. If you're trying to manually connect your Brother printer (by entering the IP address) and you are using any model other than the 710, it will not print. If you have the Brother 720, 810 or 820 and need to connect, you will need to do so by selecting the printer from the list on the main Printer Selection page (not by manually inputting). We are working on a fix for this right now so you will be able to manually connect to these printers soon.
If you have a network setup that requires you to manually enter the IP address of the printer and you need the ability to do this before the weekend, email our support team and we'll get you on a beta version of the app.