Customer looking for guidance! Hiring food trucks vs. inviting them to a gig.

I'm wondering if there's a difference between hiring a food truck for catering vs. inviting them to the event. Looking at a few food truck websites, I assume that hiring one means that the organiser pays a fee, and they cater the event. However - what I'm doing is organising a large music gig and want food trucks to be there - but people pay for their own food and the food truck keeps their earnings. Basically, run their business at my event.

Is that something that exists? Is there a name for what I want, and can I ask food trucks for this service?