The next page of the same fight: "A ray of fire exploded from her fingers and traveled with blinding speed towards her target, it exploded against the cultist's chest and quickly made his body and clothes catch on fire. As the flames spread, they hit the web, which immediately caught on fire and thrusted the other cultists into a roaring inferno of flames."
It's either that something "is on fire" or "catches fire". "Catch on fire" doesn't work. I also added a few commas to places where they were missing (the first part is an adjunct of time ("as the flames spread" and the other is a subordinate clause ("which ..."), so the commas are obligatory).