Auto-printing in Prime works with both Browser printing as well as Seamless printing. In browser printing when the status is changed, a browser print popup is shown. This is not preferred because it’s slower, and is a bit disruptive.
With seamless printing on status change, print will be issued automatically in the background without a popup. 

Seamless printing 

Here's a step-by-step guide for enabling seamless printing in Prime web.

1. Go to Session settings from the Order Tracker view.
2. Head on to the Printing tab.
3. Install Qz-Tray on your system if not already.
(Prime supports seamless printing via a utility called Qz-Tray. Download links are available in Prime.)

Once downloaded, installed and running, Prime will be able to issue print commands to the printers directly without a browser popup. 

4. Add a printer(s) and then assign a printer to Bill/KOT respectively.

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5. Hit save and you're done.

Once setup, clicking on Bill Print will send the print commands directly.
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Seamless printing can be enabled for any printer which is connected to the system. Once the printer has been connected and configured on the system, the printer name will show up in the Add Printers tab. Printers can be connected directly, via Bluetooth or via the network.