the correct grammatical use of "gratuliere"
When wishing someone a Happy Birthday, I would have said, "Ich gratuliere dich zum Geburtstag". My brother tells me the verb gratuliere operates differently to other verbs with the dative use (?) and the correct expression is "Ich gratuliere dich zur Geburtstag".
Is my German at fault (again)? I must confess it's more likely that I'm in error...