Apostolic- believes the Oneness, while most of the Mainline Pentecostal are trinitarian

god obviously

Apostolic generally refers to churches that adhere to the teachings of the original apostles of Jesus Christ. Pentecostal churches are characterized by an emphasis on the gifts of the Holy Spirit, such as speaking in tongues and divine healing. While some apostolic churches may be Pentecostal, not all Pentecostal churches are apostolic in their beliefs and practices.

Though both are Pentecostal, the UPC is Oneness and follows the apostolic teaching, while Assemblies also follow The Bible, but believe in the Trinity.