Spell Liminality

Your Patron grants you the ability to reclaim a previous failure. When you cast a Warlock spell that misses a target with a spell attack roll or when a target succeeds on a saving throw against one of your Warlock spell slots, you can use your Reaction to restore one expended Warlock spell slot. To be eligible the spell must target only one creature. Any additional spell slots gained in this way are lost when you finish a short or long rest. You can use this ability a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Your spell save DC increases by 1.