The printer jams on a Saturday and the owner asks whether the phone is enough. Sometimes it is. The question is not paper versus a screen. It is whether the customer was given the bill, and whether you can still produce that same bill in a year.
What the rules actually ask for
A VAT-registered person has to issue a tax invoice. The Value Added Tax Act, 2052, cares about the particulars of that invoice: who sold, who bought when that matters, what was sold, the taxable amount, the VAT, and the total. IRD has also been moving named taxpayers onto its own electronic billing. That duty lands on the people IRD has told, not automatically on every tea glass in the country. If you have not been notified, do not throw the printer away because a blog said paper is over, and do not buy a printer because a blog said paper is compulsory. Ask whether your PAN is on the electronic-billing list, and read the answer again when the circulars change. This paragraph will go stale. The Act will not announce that here.
For a shop that is not VAT registered, the document is still a bill with your PAN and a number, or it is not a tax invoice at all. Pasal will print Payment receipt and say so when the sale is unpaid, or when there is no PAN, or when the series has not issued a number yet. A PDF of that receipt in the customer's email is the same document as the roll. A WhatsApp line that says "got 450" is neither.
What is worth printing
Print when the person in front of you wants paper, when a business customer needs a slip for their own file, or when you are VAT registered and you have not yet confirmed that a screen copy satisfies the officer who visits you. Skip the roll for the regular who already has the bill on their phone. The series is what you must not skip. A missing number is the thing that looks like a missing sale.
The printer, if you want one, is a copy machine. 58mm or 80mm is the hardware choice. PAN bill or VAT bill is the legal choice, and it is the one to get right first.