The adjective contingent can be used to describe when something can occur only when something else does first. Making money is contingent on finding a good-paying job.
When something is contingent it means that the possibility of an event or situation depends on another happening or being true first. For example, sometimes people want to buy a new house but they make the purchase of the house they want to buy contingent upon someone else buying their old house first. That way they don't end up owning two houses!