AFAIK it's a bank guarantee YOU provide.
I couldn't, and WOULDN'T anyhow (why would you if current on type with so many opportunities elsewhere ? ? )
They are pulling a bit of a flanker by stipulating that although based in BRU with JetAirFly, you can expect to spend some time in MAK with Jet4You.
Suspect that may be why some have told them to take a hike
They used to (10 years ago) be a half decent agency, but like PARC, they seem to be going rapidly downhill to join so many other mercenary half wits operating in this sector.