Japanese speakers
Mistake: Pronouncing each word fully as "PUTTO ITTO ON", with three separate stress groups and hard [t] consonants.
Why: Katakana-based English preserves each syllable with a vowel and blocks the flap-t reduction between vowels.
Fix: Say it as one word [ˈpʊɾɪɾɒn]. Both t's become flaps (short d-like taps) because they sit between vowels. The whole phrase compresses to two beats, not three.
Korean speakers
Mistake: Producing clear aspirated [tʰ] for both t's, giving a heavy staccato "PUT-IT-ON".
Why: Korean ㅌ is aspirated and Korean prosody favors clear syllable boundaries.
Fix: The American flap-t is very close to Korean ㄹ (light single tap). Try [ˈpʊɾɪɾɒn] — a soft tap on each t, no aspiration. In British RP, the t's may stay as [t], but linking is still continuous.
Spanish speakers
Mistake: Voicing the final n of "on" or dropping it, or overshooting the flap-t into a full Spanish [ɾ] (like in "pero").
Why: Spanish [ɾ] is a well-defined tap; English flap-t is even shorter and less prominent.
Fix: The English flap is quicker and lighter than Spanish [ɾ]. Keep it minimal and the n of "on" as a clean [n]: [ˈpʊɾɪɾɒn].