Thank you for using the Support Forum. You are correct the cartridges for the WorkCentre 3550 are different than the ones for the Phaser 3300. Though they may look similar they are not interchangeable you will need the product specific cartridge. If you have further questions please consider contacting your support centre for further assistance.
I believe I have solved my own issue. They were using cartridges for a Workcentre 3550. And they are not compatible with a Phaser 3300. Is this correct?
I have 2 new toner cartridges have tested on 2 mfp 3300 's and it says install toner for both cartridges on both printers. The old toner is detected and says low toner. What could be the issue ? It seems to be the cartridges.