Everyone should be sorted out now. For people who purchases this from itch.io directly, If you go to "My Purchases" then click "Download" under Spell Casting you will see a button labeled "Get Steam Key."
If you got this from the groupee's indies unite bundle, you need to go to groupees to get the key.
If you got this from some other place, not itch.io or groupees, then you need to contact them. Mostly because they are reselling keys and that sucks.