new 
    Checkpoint[MAX_PLAYERS],
    bool:DoingJob[MAX_PLAYERS];

public OnPlayerConnect(playerid) {
    Checkpoint[playerid] = 0, DoingJob[playerid] = false;
} 

public OnPlayerSpawn(playerid) {
   SendClientMessage(playerid, BLUE, "Go to the checkpoints to do your job.");
   SetPlayerCheckpoint(playerid, x, y, z, other parameters);
   DoingJob[playerid] = true;
}

public OnPlayerEnterCheckpoint(playerid) {
   if(DoingJob[playerid] == true) continue;
   switch(Checkpoint[playerid]) {
     case 0: {
        SendClientMessage(playerid, BLUE, "You've entered your first CP");
        Checkpoint[playerid] ++;
        SetPlayerCheckpoint(New coordinates and params);
     }
     case 1: {
        SendClientMessage(playerid, BLUE, "You've entered your final CP");
        GivePlayerMoney(playerid, 500000); // The pay at the end.
        Checkpoint[playerid] = 0;
        DoingJob[playerid] = false;
        DisablePlayerCheckpoint(playerid);
     }
   }
}

#define job1 (then the cordinates)