Zebra Bluetooth printers such as QLN420 need to first be set up to connect over Bluetooth
You will need to download the Zebra Setup Utilities program
https://www.zebra.com/us/en/support-downloads/printer-software/printer-setup-utilities.html
Setup Bluetooth on Printer
Connect the printer via a usb cable to a Windows computer, then run the Zebra Setup Utilities.
Once your printer is discovered, run "Configure Printer Connectivity" , select Bluetooth and keep the default settings.
Add Zebra Browser Print to device you want to print from (i.e. Android phone)
Download the Browser Print here
Install Browser Print to all devices that you wish to have access to printers, Pallet Connect will then be able to detect connected printers
Add Bluetooth printer to Zebra Browser Print
Open Browser print and select manage device, then click "add" (+)
Change the type to Bluetooth and enter the Bluetooth printers mac address. - This is found on the printer under the blue tooth settings and will look something like A2:45:E3:89:B2:3F - and a name for the device
Once confirmed in Browser print, it will be added to your "available devices"
Add Printer to Pallet Connect
Open Pallet Connect on the device with Browser Print running and go to the manage printer page.
Click the "Load Browser Print Printers" Button
Your Bluetooth printer is now ready for use in Pallet Connect