Here is an tutorial on how you can get the Automatic Peacemaker in just one hour!
Methods
Method 1: (Outdated of 8.0.0) Players can go on Survival and kill waves of monsters and receive 
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Method 2: Go to Time Survival and make a server. Lower the player limit to 2 only and DO NOT lock it or else you will not get coins. Once you hit 200 coins leave the match and let the other player take care of rest of the monsters.