@Ravco, tthurman is referring you to VPCabs support because the option to enable or disable the coin button does not exist within GameEx. If there is some sort of shortcut key to do so, it is related to either your remote keyboard or some other software running on the machine. If you read the manual, VPCabs is the distributor and/or warrantor of the machine.
Within GameEx, the input command setup controls navigation within GameEx, but not for the games. GameEx is an emulator launcher. Once the game is launched, control is passed to the emulator and the settings within the emulator are what dictates how the buttons and joystick will work. If your cabinet is running arcade games, most likely it is using an emulator called MAME (Multiple Arcade Machine Emulator). I will mention that there is an option within Mame setup called Free Play (I believe) that will disable the need for coins. After launching a game you can press Tab to enter the Mame Setup and then check the Global parameters. I will also mention that if you are not familiar with configuring Mame, take great care while you are in the Setup. A miskey there can cause a lot of headaches.
Contacting VPCabs really is the best option for correcting your issue.