"Moreover, brethren, I declare to you the gospel which I preached to you, which also you received and in which you stand, by which also you are saved, if you hold fast that word which I preached to you—unless you believed in vain. For I delivered to you first of all that which I also received:
that Christ died for our sins according to the Scriptures,
and that He was buried,
and that He rose again the third day according to the Scriptures,
and that He was seen by Cephas, then by the twelve.
After that He was seen by over five hundred brethren at once, of whom the greater part remain to the present, but some have fallen asleep. After that He was seen by James, then by all the apostles. Then last of all He was seen by me also, as by one born out of due time. For I am the least of the apostles, who am not worthy to be called an apostle, because I persecuted the church of God. But by the grace of God I am what I am, and His grace toward me was not in vain; but I labored more abundantly than they all [i.e. all the other apostles including the apostle John], yet not I, but the grace of God which was with me. Therefore, whether it was I [Paul] or they [the other apostles], so we preach and so you believed." (1 Cor. 15:1-11, NKJV)
The apostle John preached the same gospel as the apostle Paul!
What gospel are you preaching?