It's a phrasal verb. Sometimes a verb and a particle belong together to convey a certain meaning, just like the meaning of "put up" in English means something different that just the words put and up. That's also what's going on here with the phrasal verb tycker om, which means "likes" here.
The "type what you hear" exercises currently have a bug where typos aren't displayed to users. What you wrote is not accepted in the admin interface; it just let you through with typos. Obviously, this is extremely detrimental to people's learning, and I really hope they can fix it soon.