There are a few rules to use SkipTax and tax refund in general :

You must be at least 16 years old
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You must live outside of the European Union (So British and Swiss citizen are eligible for exemple)

You need to export back to your country all the items you ask a tax refund on, and they need to be in brand new condition when you leave.

You must ask the stores an invoice with SKIPTAX'S NAME on it, in order to get the refund on the items you bought (except in a few partner shops like Disneyland Paris)

You need to buy the items in France or have them delivered in France.