Is this broken or user error?

Hi! I have not a clue about anything fishing-wise, but my grandpa recently bought this fishing reel and he said he couldn’t get the cap to stay on. Supposedly, when you press the button at the bottom, it’s not supposed to pop off. But no one in my family can get the cap to stay on.

Is it just user error? Or was the reel broken from the start? We think it may possibly be stripped or something is broken, but alas I have no clue 😅 It’s a Zebco 33, I don’t know anything else beyond that.