with the new patch they disabled the replay missions button HOWEVER there is still a way to replay missions
At level 15, players will gain access to a job named Violent Duct. It is a brief mission, in which players kill a gang, steal their dropped drugs and then deliver them to their employer. The mission can be done in as little as 45 seconds if you're moving fast and yields $9000. Repeating this mission can net you over $400,000 per hour. Players who are below level 15 can still help out in the mission also, so long as the leader is above the required level and can activate the mission. If you are looking for fast, easy money, it is highly suggested you seek this out and repeat it as often as you can tolerate it.
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It might seem that as of the most recent Title Update, the ability to replay this(and other) jobs has been removed, but this is not the case. After the mission has finished, like/dislike/no vote the mission as usual, but instead of hitting the proper button to continue, hit the "fire weapon" button (RT on Xbox 360) to repeat the mission
How to Make Money in GTA Online - GTA 5 Wiki Guide - IGN
