After some research, the toner cartridge looks very similar to the one used by the Lexmart E260, E360, and E460 printers.
https://www.etoner.ca/images/LEXMARK%20-%20E260%20COMPATIBLE.gifI take it that you just can't put in a Lexmark original toner because the toner chip on the cartridge won't allow it to work even of they are identical.