There are a few possible reasons why your Brother printer might be printing blank pages even though it has ink. One possibility is that the ink cartridges are not properly seated in the printer. Another possibility is that the printer's nozzles are clogged.
If you think the ink cartridges might not be properly seated, try removing them and then reinserting them. If the printer's nozzles are clogged, you can try running a nozzle check to see if that clears the problem. You can also try cleaning the print head.