What was this episode? Police procedural series?

I watched an episode of some police show (like FBI, SWAT, Rookie Blue, LA's Finest etc) a few years ago, possibly late 2010s, or very early 2020s. There was a female undercover agent who was smoking weed with a gang member, I think warning him that another gang were about to attack. At some point I think she admitted she was a police officer but he already knew. She may have been from a crossover series,I don't think she was a main character. 

The male main character met the black gang leader possibly at/after a funeral. They knew each other from years ago and seemed to begrudgingly respect each other. I think the gang leader's right hand man was his cousin (nephew?) and a bit later the cousin messed up so the leader had him sealed inside a plasterboard wall. He was released after a while and the leader said that was because they're related. 

I think it was based in somewhere like LA/Miami, somewhere hot in America.

I've tried reading episode summaries for different series but cannot work out what series this was. If anyone recognises it from my rubbish description, I will be so happy!