I have a modest balance remaining on a UATP card from a flight that was canceled during COVID circa summer 2020.

I want to completely spend down the UATP card balance. However, I can't seem to make the payment selection work for this on the AC website.

Am I able to call into Air Canada to do a booking, to spend the remaining UATP amount, then pay for the rest either using a credit card or an AC gift card?