Boon of High Magic

What modifier did you add to make this function? Or do you just keep track of it manually?

I am trying to create a similar boon for my players, but I cannot figure out how to make it work properly.

Heya - it doesn't add a new spell slot for the character in the spells section - just a check box next to the feat in the features and traits tab that you would check when the character uses the spell slot granted by the boon. So yes... manual basically. I forgot how I did it since it was a few years ago but it wasn't particularly complicated. Cheers!