Many churches today teach that responding to the gospel is merely mental, and not necessarily behavioral. This is a different gospel. Fortunately, Keith Green’s article on this topic is still available on his wife’s website:
Also, Dan Corner exposes one type of a “license for immorality” false version of the Gospel at:
Easy believism is often combined with “Once Saved Always Saved” to present a lethal false Gospel presentation. This site exposes “other gospels” such as this. But that does not tell us what the Gospel IS.
For more research on what the Gospel is you can read a more scholarly debate on the matter.