Thanks for your prompt response, @abricoetzer.

I appreciate your screenshots a lot. It helps me provide an accurate solution to your concern.

You can change the label Amounts are from Exclusive of Tax to Out of scope of Tax. This way, the amounts on the item will be completely tagged as out of scope of tax.

Let me show you how to change it:

1. Go to + New and then select Purchase order.
2. Click the Amounts are drop-down lists.
3. Choose Out of scope of Tax.
   
4. Hit Save and close.

That way, you're able to save the purchase order seamlessly.

You can refer to the articles provided by my colleagues above this thread, @MirriamM , @FritzF , and @MaryLandT.

I'll add this article as your reference on how to apply PO to an expense, cheque, or bill: Apply a purchase order to a supplier transaction.

Please feel free to leave your message or notify me by tagging my name (@Jovychris_A) if you need further assistance. I'll be happy to help you. Have a great day!