Once again was Paul not an Apostle?
Yes Paul was an apostle.
An apostle is someone called by Jesus directly to be an apostle.
Matthew 10
1 Jesus
called his twelve disciples to him and gave them authority to drive out impure spirits and to heal every disease and sickness.
2 These are the names of the twelve apostles: first, Simon (who is called Peter) and his brother Andrew; James son of Zebedee, and his brother John; 3 Philip and Bartholomew; Thomas and Matthew the tax collector; James son of Alphaeus, and Thaddaeus;
Judas betrayed him. So he wasn't any longer an apostle.
His replacement was chosen by lot, not by the direct call of Jesus.
26 Then they cast lots, and the lot fell to Matthias; so he was added to the eleven apostles.
Leaving us with 11 total who we know had that direct call of Jesus to be an apostle.
Then Paul received his call for apostleship. Making it 12.
1 Corinthians 1 1 Paul, called to be an apostle of Christ Jesus by the will of God, and our brother Sosthenes,