To earn easy money while playing solo, successfully complete
"Medieval - Battlefield Helix Rift" to earn $8,000 base pay plus the bonus.
It only takes a few minutes to complete once you know how to complete it.
To earn easy money in Co-op mode, play the "It Belongs In A Museum" heist.
You will earn $25,000 base pay plus the bonus ($10,000 on the lower end),
and it should only take approximately five minutes to complete each time.
To easily complete the final heist mission in the Palais Du Luxembourg,
you will need at least two players -- one to get the painting and one
to distract the guards. Go around the structure through the back entrance
in the courtyard, and approach the main lobby where the lower floor painting
is hidden. There are multiple paintings in the area you need to collect.
The decoy player will need a full inventory of medicine while the thief
needs smoke bombs, ammo, and poison darts. The decoy player needs to
run around the lower floor, attracting the patrol guards into a large
group and leading them away from the paintings. Paintings can only
be collected while you are not being watched. If only a few guards
are outside of combat and waiting around near a painting, defeat them
to clear the area. Using this method does not take long, but guards
do not always follow the decoy player. The decoy player will need
to attack waiting guards and run away. Do not worry if one of the
players die during the escape, because as long as one player finishes
the heist, all players will receive the money.