If you google Paul false apostle you'll get hundreds of thousands of results. Of course, not all results contain opinions against Paul, but I estimate that at least half of them state that he departed from the true gospel of the Lord Jesus Christ.
There are also those who don't go to the extreme of calling Paul a false apostle, but regard him as "not completely reliable".
Is there any reason for us to think that Paul's authority is questionable?
Paul is not a false apostle, nor did he stray from Jesus' teachings.
Jesus met Saul on the road to Damascus, and straightway he followed Jesus, and said he did not receive the truth from other people, but from the revelation of Jesus Christ, which he did not need to have faith for he seen it as an eye witness, the same as the disciples that did not need faith for they seen it in person, and said he taught the wisdom of God, and not of man.
Paul said he did not want to know anything among the saints, but Jesus Christ and Him crucified, and said if anybody teaches another Gospel let them be accursed.
People that did follow Paul, who followed Christ, and then did not, and went back to the world he dismissed, although he wanted them to abide in the truth.
Was given an abundance of revelations that God allowed a messenger of Satan to buffet him in the flesh, so he would not get arrogant but stay humble, for God resists the proud but gives grace unto the humble, and he wanted to use Paul.
Paul got in Peter's face and told him he did not walk according to the Gospel of truth, and the disciples accepted him.
Was not arrogant but said he is the least of least of the saints.
Preached being led of the Spirit, and abstaining from sin, and rebuked people when they walked according to the flesh enjoying sins.
Preached unto the Gentiles who were in to works of their religions, and said none of those works can save them, but only by confessing Jesus by faith can they be saved, and to abandon their religious works, but then speaks the same as James and John when they are led of the Spirit, saying they have to have charity, love in action, or they are nothing, and have erred from the faith.
So Paul taught a strict moral lifestyle, and said he keeps under his body, and keeps it in subjection, which that is pleasing to God, and if a person preaches a strict moral lifestyle they would have to be led of the Spirit, for the flesh would not do that, and if led of the Spirit you are right with God, so Paul was right with God.
And Paul taught the same from the first book to the last book that he wrote.
Never abandoned the death, burial, and resurrection of Christ, never abandoned a strict moral lifestyle led by the Spirit, never advocated works that are of people's doings and not the Lord, said to feed the poor and hungry if you can, people that abandoned the truth that were with him he went against, and rebuked the people engaging in sins, taught the nations will come together having an understanding of the coming beast kingdom in the future that will rebel against God, and to not go along with them, and gave all glory to God and Jesus, and if anybody abandoned the truth of the Gospel let them be accursed, and had revelations from God big time.
Paul taught the same thing from the first book to the last book he wrote, and he was definitely led of the Spirit, and if led of the Spirit he is saved, and even when he was near to die he said, I have ran the race, I have finished the course, and he is ready to meet the Lord, which means he stayed in the truth from start to finish.
Paul did not abandon any truth, and it is funny that people say he abandoned the truth, and was a false prophet, which if we are honest Paul would make a lot of us, and I mean a lot of us, look like a casual Christian compared to him and the strictness he had to following the truth.
Whatever Jesus taught Paul taught.
But this is the icing on the cake that Paul is not a false apostle, and will surely testify Paul was not a false apostle, well not really the icing for it is obvious that Paul was not a false apostle, but adds to the fact that Paul was not a false apostle, and a very good fact indeed.
God changed names in the Bible of people to identify their new identity in the LORD, and to set them apart to follow him.
God changed Abram to Abraham, and do you think Abraham is saved.
Changed Sarai to Sarah, and do you think Sarah is saved.
Changed Jacob to Israel, and do you think Jacob is saved, and Israel not His chosen people, and Israel is still God's people, and when a Gentile is saved they become a Jew inward, and part of the commonwealth of Israel, but Israel goes through trouble because of their rejection of Christ, but God will turn the nation of Israel to the truth of Jesus in the future, and all Israel shall be saved and become spiritual at that time, where all Gentile nations will fall that rebelled against God.
Changed Simon to Peter, and do you think Peter is saved.
If God changes a person's name to another name to identify their new identity in the LORD, and they are set apart for Him, you can rest assured they are saved, for if God changed their name He also knows they will do what is right to inherit eternal life, and He will see to it.
For if God changed their name and they failed at obtaining eternal life, then God failed for the new name did not live up to what God changed the name for, so you can know they have salvation and will live up to that name.
God changed the name of Saul to Paul, so what does that tell you.
Did Abraham fail who is the father of many nations.
Did Jacob fail who became Israel, and the nation Israel God's chosen people.
Did Peter fail who was given the keys to the kingdom, and the Church was built upon him after Christ the chief cornerstone and foundation, and preached the first sermon that got the Church going in the truth.
And neither will Paul fail, and not stray, and not waiver, who is sent to the Gentiles to preach the truth to them.
When God changes a name of a person to follow Him it is iron clad they will accomplish their mission, and stay in the truth from start to death.
For these name changes is the big moments in history, and a benefit to mankind, Abraham, father of all nations, and being right with God having the same faith as Abraham, got the ball rolling there.
Jacob, Israel, God's chosen people, and everybody saved belongs to Israel, got the ball rolling there.
Peter, keys to the kingdom given to him, Church built upon him after Christ, preached the first message of salvation, got the ball rolling there.
Paul, sent to Gentiles, got the ball rolling there.
But Jesus is the greatest one, and the most favored of all, and without Him none of it was possible, who did not have a name change, why, because He is perfect according to His humanity, and God, and set apart for God before He was born, and for eternity, so no name change was required, who is the ultimate one who got the ball rolling for salvation and the truth.
But mere mortal men born in sin need a name change to identify their new identity in the LORD when it comes to a big game changing plan of God for the good of humanity.
And Paul was one of them.