You have to call to purchase and must be making a reservation when doing so.
Recent changes to the online system will allow you modify trips that have them...something that we couldn’t do before late 2020.
Once you buy, you will see a temporary contract show up at a resort you don’t own. It will be whatever resort the actual points came from.
If you cancel a trip using the points, they will show up in this contract and then you make sure to choose it when booking again. As already mentioned, they can only be used 7 months or less, and expire at the end of the UY of the canceled trip. They are non refundable as well.
I don't know if it's because I also have direct points, but I believe I saw it said elsewhere that one-time use points count as "direct" points, so they are usable at Riviera.