This is a letter he wrote to the King asking for a pay rise. He asked the king to double his pay! Not only this but the king should pay him what he missed out on when he started the job.
King Henry who is arguably one of the scariest figures in history signed and gave him that pay raise!
Not only does this show that the guy knew what he was worth but that he also had the balls to demand. Also notice how everyone is wearing the same outfit except for him! He was clearly very talented and trusted by the King because he also played at his funeral.
Just shows the first Africans in England were not slaves and held prestigious posts in Britain.