There's a 99% chance that "casting" means "fuck some scammer for free".
He's put up a tempting website - 'Look! Earn all this money!' - in the expectation that even one woman is going to turn up and, 'just to see if you're good enough for my agency', fuck him.
If you want to go along, it's up to you.
But the basic rule of Get The Money First applies to "casting" as well: treat it as a booking and you don't take your clothes off, never mind fuck him, until you have the cash in your hand.
You can always phrase it as 'if you won't pay £££s to fuck me, why do you think anyone else would?'