Stuck and couldn't start The Merryweather Heist [duplicate]

Trevor mentioned doing some flight training before starting the heist, which I did, but I haven't received word from Trevor about starting the mission. I read online that Michael's flight training and Franklin's shooting range training are optional, but I still have no indication on how to start the heist on my map. (The only marked missions are Lester's, which I'm leaving for later.) Is this bugged?

Solution 1:

Lester's first assassination mission done first will advance your game to the point of progressing, and having him call you.

When I was trying to progress the story, I had done all regular and side missions, but left Lester for last. My game had nothing else to do, so I completed his mission. Immediately afterwords, I got a call allowing me to attempt the heist.