For printing from an iOS device (Iphone, Ipad…), you must use a network printer and create a port redirection on your router.
When your router receives a document to print, it will reroute it to the specified printer.

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1/ Login your router (or Internet box) setting page and find the section to add a port redirection.
Add a redirection from the port 9177 (it can be any other external port open on your router) to the port 9100 (printing port) in TCP protocol on your printer IP address.

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2/ In the 'Settings/General Settings/Printers & receipts' section of your account, add in the 'Receipt printer' field the printing port used (9177 in our example).

Now, you should be able to print receipts from any device connected to your network.