If your parking stay qualifies for tax exempt status in your state, you will only be able to make a Pay Later reservation.
You will then need to check out with a cashier and provide your tax-exempt form. The cashier will then apply your tax exemption to your stay.
You will need to show your tax-exempt form at checkout with the cashier for every stay that should be tax-exempt.
You will not be able to save your tax exempt form to your Spot Club account.