So in my D&D world, originally only a mortal on the prime material plane could contact a demon to form a contract, but now the demons have a foothold in the world and can start offering contacts to many more people.
How did this happen, you may ask. Someone in need contacted a demon, and that demon seized the opportunity.
That person was an architect who was running out of time to finish a building. They were expecting to have to give up their soul, or their firstborn child, but it ended up costing them a lot less. The demon simply asked for the architect to build them a house for it to live in.
However, I need the contract to be formulated for this ambiguity to work: when the demon asked for a house to live in, it actually meant that the demon could then stay on the prime material plane, as it had been "allowed" to do so. Once that demon had an anchor in this world, it then allowed many more to come through from hell, and to form more and more contracts with mortals. This in part explains why there are a lot more demons and warlocks in the world than angels and angelic warlocks.
So, how would you word this contract between a sneaky demon and an architect?