Hey there @SeamusYarr
Adding Reward Points is working for me here, be sure to do the following :
1- Type In the amount of points you'd like to use in the "Use reward points ( xxx available )" text box.
2- Click on the Plus icon to add your points.
3- Your reward points appears on your purchase & the new price is calculated.
4- You can remove them clicking on the Remove reward points box.