Tilt code 55 is preventing the game from going into the “Ready” mode. The bill stacker /cash can is not being detected. If it is installed, be sure the release lever (inside the stacker door) is fully in the latched position. If you never had a can installed and it used to work; something deleted the bypass that was done. Either mechanically alter the micro switch arm or bypass the wiring properly.
Of course, their could be a MPU board or bill validator issue causing the Code 55.