AP is not anything similar to EP. They are very much unrelated. AP was just recently used by rising rap stars during the 2010s.
AP might simply be used to refer to the assistant producer. It is an acronym for it.
“My AP is the best because he handled everything while the main producer bailed.”
However, Post Malone, Rich the Kid, Migos, and many more used AP to point towards Audemars Piguet, a specific brand of luxury watches. These watches have become a symbol of power, fame, and clout. If you have one of these, you have made it in the rap world. Follow these examples for better usage:
“I heard some rapper got his AP stolen.”
“My mom will buy me an AP after my songs get streamed 1 million times in Spotify.”