You have made a deal with The Cabal; in exchange for a small slice of your soul:

You may regenerate some exhausted spell slots as a bonus action. The spell slots you can regenerate depend on your caster level. Once you have received this benefit, you may not do so again until you complete a long rest.

You may regenerate up to a total cost equal to half your caster level rounded up, dispersed as you see fit. You can regenerate spell slots no higher in level than 5th, and you may only regenerate exhausted slots.