I don't think I've ever gotten key 28 to work on an 044 legacy adapter board. You are supposed to use key 40. I've never used key 37. Attached is the PSR for your base chip. In the section that says Maximum Bet, it says:
To select the maximum number of coins or credits that can be wagered per game, access the Key Chip Menu and touch Max Bet Setup and the appropriate icon. To view this option’s setting, access the Operator Menu and touch Setup, Game Options, Max Bet Setup, and the appropriate game icon.
Typically, the max bet is determined by Jurisdiction, denomination, and game. It is possible that your only choices are 20 or 40 based on configuration. What denom do you have the game set to?