Ontario Highway Traffic Act

I received a ticket in May while I was driving a company pickup truck, towing a trailer. The ticket was issued for Highway Traffic Act Sec. 85 (1). OPER/PERMIT VEH FAIL DISPLAY.
I had no idea that a sticker was required and my employer didn't tell me one was required. Shouldn't the Owner/Operator be responsible for the sticker?
As the driver, do ...