Temporarily change the product type to Variable Product and set the Tax Status. Then before you click the blue Update button switch it back to PW Gift Card. Then you can click Update.
Keep in mind that you are now collecting double tax (once on the gift card, then again when redeemed) so you will need to handle not charging tax when a gift card is redeemed if you want to avoid this.
The law states that tax should only be collected on a gift card purchase if it is for a specific product or service. Our plugin lets you redeem a gift card for anything so by default we don’t collect tax until they redeem something.
This also takes care of the recipient being in a different country from the purchasing customer in case tax rates are different when they redeem.