I asked the AI to be sure:

on won what letter does the “AI” start in “IPA”?

The “ai” sound in IPA (International Phonetic Alphabet) starts with the letter “a” in the combination “aɪ” which represents the diphthong sound like the “long i” in words such as “buy,” “aisle,” and “isle.” The IPA sequence “aɪ” begins with the letter “a” and is followed by the letter “ɪ” to form this diphthong sound. So, the “AI” sound in IPA starts on the letter “a.” This diphthong consists of two vowel sounds pronounced in one syllable, starting with an open front vowel [a] and gliding to a near-close near-front vowel [ɪ].

So, it’s confirmed. The “AI” is there where “IPA” has an “A” followed by an “I”.