Error:Printer halted. kill() called!
Your G-code file contains the G28 command to home the printer, as you do not have endstops, execution of this command fails. If you do not use endstops, you should never home the printer, instead you must position the print head at the origin yourself (generally this would be at coordinate [x=0, y=0, z="paper thickness"]) and remove homing commands from your G-code file.