|This is one of the setup missions for the FIB Heist, which is called Blitz Play. Prior to starting the setup missions, you should get a text from Steve Haines that says for all three of the protagonists to meet them at the usual spot. This places a "B" marker on the map, which initiates a cutscene with the same name as the heist.|
Once the cutscene ends and you leave the area, you will be in a conference call with the other two protagonists, after which multiple mission markers will appear on your map. Go to the marker at the Vespucci Beach area, where you will find a shop that sells masks. You need a mask for each character, although it doesn't really matter which ones (three white hockey masks will fulfill a challenge). Once you buy them, the mission will end.