“Pūrimatālā, near Ayodhyā, under the Akṣhayavaṭ tree” is remembered in Jain tradition as:

• A Kalyāṇak-bhūmi – a holy place where important auspicious events of Tīrthankars happened.
• Pūrimatālā is described as a town/region connected with Ayodhyā. Some scholars identify it with the area of Prayāg / Prayāgraj (Allahabad).
• The Akṣhayavaṭ is a very ancient, famous banyan tree there, considered “undecaying” (akṣhaya = imperishable).

According to Jain literature, Bhagwān Ṛṣabhadeva (Ādināth) attained Keval-jñān (omniscience) near the town of Pūrimatālā, while sitting under a banyan tree in a nearby forest. Traditional descriptions connect this with the sacred banyan known as Akṣhayavaṭ.

So in simple words: This phrase is pointing to the holy spot near Ayodhyā (identified with the Prayāg region), under the eternal banyan tree Akṣhayavaṭ, where Bhagwān Ṛṣabhadeva’s important spiritual event (Keval-jñān) is believed to have taken place.