Printer Repair Questions? Ask IT Technicians for Answers ASAP
If the printer is still saying that the toner needs to be replaced, then either the toner cartridge is defective or the sensor in the printer is not detecting it.
Ensure you are using a new, genuine Brother cartridge, and not a third party or refilled cartridge.
Try removing the cartridge and cleaning out inside the printer, then reinsert the same cartridge or a new one.
Let me know how you get on.