Some disregard the authenticity of Paul's apostleship because Matthias, the replacement for the traitor Judas, was appointed as the 12th Apostle long before Paul’s conversion.
There is no written record of God or Jesus confirming Paul's apostleship. Watch this short vlog then listen to the full podcast of the same name for more details.
While so many of us cling to the Apostle Paul's example and teaching, others are repelled by him and label him as a self-contradicting, hypocritical deceiver. Who is right?