Can't register my MF743C printer on support site.

[sdmund]

Every time I try to register my printer on the support site it says the SN isn't correct. I can't find any other number as detailed in "how to find my serial number."

[shadowsports]

Greetings,

Look at your box.  The serial number is on the side (sticker).  If you don't have the box any  longer, you can view the S/N in the Remote UI

What is the exact error message you are receiving in the MyCanon Portal?