。
Everything went off without a hitch.
Literal
All-things trot-trot rhythm [adverbial-に] went.
トントン拍子 is a colorful idiom meaning 'going smoothly, without a hitch,' literally 'tap-tap rhythm.' The mimetic トントン ('tap-tap,' the sound of rhythmic knocking) conveys brisk, regular progress. 拍子 ('rhythm, beat, tempo') anchors the image of steady advance. A lively, slightly colloquial way to report success.