Dark mana grimoire?

[Jon.Topps]

I just got dark mana. In the one page it says I need a crazy amount to unlock warlocks, but that this will likely be done through contracts. However, its says I can use the little bit I have to unlock a grimoire. There is one grimoire that has a low cost of dark mana, and no other cost. However, it doesn't let me buy the stupid thing!
Summoning the undead costs 13, and I have 84.
Why doesn't it work?

[aruth]

You also have to buy a slot on the right side of the page for the spell to go into.

[Jon.Topps]

Cool thanks! Is there a way to remove one from the right page, so you can swap it out? I have enough for the fish now, but I can't get the hand out of there. I know you can buy two more slots, but there's six items. Certainly you can swap them out somehow?

[Gummy Bread]

spells can only be removed upon reset. Your choice matters per run, and you'll only have 3 (eventually 4) out of six spells per each spellbook page.