Auntie to Aunt, is like Mommy to Mother.
They refer to the same person,
but one is an affectionate expression of endearment,
while the other is the more formal word.
If Duo did not accept you answer,
it is probably because there is a different word in Italian that means "Auntie\Aunty" - Zietta.
• [EN] Mother = [IT] Madre.
• [EN] Mom ⠀⠀= [IT] Mamma.
• [EN] Mommy = [IT] Mammina.
• [EN] Aunt ⠀⠀ = [IT] Zia.
• [EN] Auntie ⠀= [IT] Zietta.
Not a native speaker, but I'm sure it's plain "sia" or "zia". Although there's a hint of tzia in the 4th example in your Forvo page, the full sentence "La sorella di mia madre è mia zia." The "tz" is obligatory in a double z word, like tazza - https://forvo.com/search/tazza/ I think with the single z in zia Italians just make a very slight adjustment to the sound depending on what comes before and how fast they're talking. I think when your pronunciation gets good and you speak quite quickly, it will just come out right .. your lips will want to make the zia clear and it will just happen, softer z or harder tz. Ciao !