Tax

Manage → Settings → Tax (vi: Quản lý → Cài đặt → Thuế) is off until you turn it on. Once it is on, every order your shop takes is taxed.

The most important question is not the rate

It is whether prices already include the tax or the tax is added to them. The same rate on the same goods produces two different amounts:

• A 110,000₫ order, 10% included → 10,000₫ of tax sits inside that price. The shopper pays 110,000₫.
• A 110,000₫ order, 10% added → 11,000₫ of tax goes on top. The shopper pays 121,000₫.

Getting it backwards raises no error. It produces an order 10% above the price the shopper read on the page — which they find at the payment step, and which you find as an abandoned cart.

In Vietnam a shelf price is what the shopper pays: the VAT is already in it, and an invoice breaks it out rather than adding it on. So the default is included, and it is almost certainly what you want.

What you call it

The label field ("VAT 10%") is snapshotted onto every order. So renaming it, or changing the rate next year, does not rewrite this year's invoices — an older order keeps the figure and the name it was actually charged under.

Per-product tax classes

Vietnam taxes most goods at 10%, some at 5%, and a real list at 0% — books, unprocessed food, several medical supplies. A shop selling one kind of thing can stop reading here.

A shop selling several creates tax classes: a name and a rate. Each product then picks its class at Manage → Products → (open one) → Tax class. A product in no class is taxed at the shop's own rate — which is every product you already have, until you change one.

The class picker only appears once you have created at least one class. With no classes there is no question to ask.

A 0% class is a real rate, not a blank. "Không chịu thuế" means 0%, and it is charged as exactly that rather than falling back to the shop's rate.

An invoice with more than one rate

An order whose lines carry different rates shows one line per rate, not one combined line. An invoice reading "VAT 10%" beside a figure two thirds of which was not taxed at 10% is an invoice that lies — and ending that is the whole point of classes.

Delivery on a mixed order is taxed at the shop's own rate.

Editing an older order

Change a quantity and save, and the tax is recalculated at the rate recorded on that order, not at today's setting. An order placed last year and edited this year is still taxed at last year's rate — which is why the rate is stored on each order in the first place.

Deleting a tax class does not re-tax orders already placed under it either. It only changes what a product still pointing at the deleted class is taxed at from then on: the shop's own rate.