The Early Church Fathers often through this phrase around, as does St. Paul in his letter to the Galatians (verse 9).
“As we have said before, and now I say again, if anyone preaches to you a gospel other than the one that you received, let that one be accursed!”
I would like to continue going down this rabbit hole in the writings of the Early Church Fathers, where they used this term anathema and what false gospels were specifically being taught.
There are Protestants & Evangelicals who claim that this verse is specifically speaking to the Catholic Christian Church, which is more based on their misunderstanding of what we believe (or what they think we do not believe).
There are also some in this forum who hold to what I would call false gospels, but I would like to focus on what the early Church was specifically referring to. I have a feeling there will be some overlap.