It isn't mandatory, but commission for the piece would be very, very appreciated. No matter what the task, it's always better when you get paid for doing it  It would also bump your piece up to the top of the waiting list (I should probably mention that in the OP...). What that commission would be would be entirely dependent on what you want for the piece. For example, a solo piano piece would cost less than a full orchestra piece.
And yes, Steel. I PayPal, bro.
And yes, Steel. I PayPal, bro.
"When the power of love overcomes the love of power, the world will know peace." -Jimi Hendrix