Canon Starwriter Jet 300 word processor ink cartridge problem

I’ve got an old Starwriter Jet 300 that was working fine until it ran out of ink. After putting in a new cartridge, I keep getting an error saying the cartridge isn’t installed properly, but it clearly clicks right in to place.

Anyone have any suggestions? It’s really the perfect device for my mother (computer illiterate) to use and would like to get it working again.