First things to do

Datetime and Security

Let's make sure that the device is running the latest version of Android (this can usually be done in the last menu option under System Updates in the Android settings). 

In the Android settings, find Date and Time and verify that the time zone is set correctly (Europe/Amsterdam or Europe/Budapest), and that automatic time synchronization is enabled.

For certain tablets, it is necessary to enable the option for Unknown Sources, which can be found under the Android settings, in the Security section.

Wireless connection

The client device needs to be able to reach the server over the Internet. In the case of WiFi printing, client isolation should not be enabled on the network. Brother printers typically only support the 2.4GHz band.

Sunmi mobile printers

Sunmi V2s devices are initially set up for handling normal (non-adhesive) paper by default. In the Android device settings, this needs to be set to "Label mode."

Zebra printers

For Zebra printers, the printer needs to be initially configured for the correct paper size, gap setting, and final output. (Later on, using a USB connection, the application will be able to do this automatically.)