“Doctrinal Beliefs…Oneness Pentecostal Sources of Authority.”
Oneness Pentecostals of all branches affirm the authority of the Bible for doctrine. Many, however, utilize only the King James Version to proof text their unique doctrines. In addition, many Oneness advocates rely on the unbiblical revelations received by various Oneness leaders whom they regard as divinely inspired or anointed interpreters of the Bible. For example, many in UPCI consider the writings of Frank Ewart and John G. Scheppe as authoritative.
Biblical Response: The Bible is the inspired, inerrant, and infallible Word of God (see 2 Tim. 3:16-17; 2 Pet. 1:20-21). It is the final authority for the Christian on all matters of faith and doctrine. No single translation or human interpretation can be regarded as infallible. All modern writings or “revelations” must be analyzed in light of sound principles of biblical interpretation.
Only One God:
Oneness Pentecostals declare that the Godhead consists of only one Person and deny the traditional doctrine of the Trinity. They maintain that the only real “person” in the Godhead is Jesus. Thus, they are often referred to as the “Jesus Only” Movement. They maintain that God exists in two modes, as the Father in heaven, and as Jesus the Son on earth. Nevertheless, they are the same person, not two separate persons. The Holy Spirit is not regarded as a person at all, merely a manifestation of Jesus’ power or a synonym for Him. Several verses are quoted to establish this view, such as Colossians 2:9 (NKJV), “For in Him (Jesus) dwells all the fullness of the Godhead bodily.” Oneness theologians would argue that if the Father and the Son were separate, then the Godhead could not fully dwell in Christ. Matthew 28:19 also affirms their views that Jesus commanded His disciples to baptize in the “name” (singular) of the Father, the Son, and the Holy Spirit.
Jesus is said to have two natures: human and divine. Thus, when He died, only His human nature died. Also, when Jesus prayed, it was His human nature praying to His divine nature-not to a separate Father in heaven.
(More Info from: https://www.namb.net/apologetics/resource/oneness-pentecostalism/)