Try asking first if he’d like it, if so, either give it as an unconditional offering, or promise it to him on the successful completion of the mission or task.
He’s not usually shy about showing he wants something. 
This may be useful: How To Delight Belial 🖤
(Also, mod hat on, your topic got a bit derailed earlier, I have now removed those posts and stripped this back to be purely on-topic.)