Is profit based on drawing overturned cards that contain different numbers considered unlawful, even with the mutual benefit and consent of both parties?

The aforementioned transaction is impermissible and its contract is invalid, because the wage involved is unknown, as it is not known what the employee will receive from the papers with varying numbers, which makes the contract concluded on an unknown wage. Furthermore, it contains a semblance of gambling due to its reliance on chance. If the transaction is completed, then the employee is entitled to the wage customary for such work.