Was the assignment listed in Canvas (or whichever platform the professor uses)? Did you check all of your emails and Canvas notifications? Did your grade page list the assignment with a 0 grade? Have you asked any of your classmates how they were notified about the assignment? I never listed all of my assignments on my sylabi, just types of categories and percentages. Longer assignments and projects had a rubric; this was usually communicated once with details about the due date. Canvas has made this so much easier; is it listed on the assignments page? Do you still have access to the class? Your professor will (most likely) be able to provide proof of notification/assigment listing, which will not go well for your appeal. Research what you can and let us know.