The term bet can be used in a few different ways, but generally means "agreed" or "okay". For example, if someone says "Wanna grab lunch later?" and the other person responds "Bet", it means they agree to the plan. Bet" can also be used as a response to confirm that a statement is true.
As ESSENCE previously pointed out, Perry still holds minority stake in BET+, and works with the network to house a large number of his productions. Perry and BET have been in collaboration for quite some time, as the network helped fund his first feature, 2005's Diary of a Mad Black Woman.