"I am experiencing the exact same issue, but I didn't quite understand what you meant. Look, this line is related to Ultimate Backup, and these lines were already present in the .ini file: Ini, TOML (Fire),Ambulance,FireTruck,LocalPatrol
(Medic),First Responder
GroupBackupUnits=First Responder
I figured out that I need to replace the First Responder section with the spawn name of my downloaded car model. However, while this applies to the Medic category, I can't find a "Fire first responder" option under Fire. I also have another question: What exactly does GroupBackupUnits=First Responder do? And what happens if I change the First Responder option to the name of an Add-on car?"