Zip codes belong to a state/province, and delivery pricing cannot be saved for a state that does not exist on your account. If the radius reaches states you have not created, the save is refused and a panel Add these states first lists each missing state with a tax-rate box (default 0 %). Enter the sales tax rate for each and press Create states & save pricing; Sprwt creates the states and then saves the pricing in one go. You can later edit the states on States & sales tax.