According to inscription on the stele of Sdok Kok Thom, Indrapura was the first capital of Jayavarman II reign about 781, before the foundation of Khmer Empire in 802.
George Coedes and Claude Jacques identified it with Banteay Prei Nokor, near Kompong Cham, Cambodia, while Michael Vickery assumes it was closer to Kompong Thom.
References
Indrapura (Khmer) Wikipedia(Text) CC BY-SA