3. modal verb. If you say that something should have happened, you mean that it did not happen, but that you wish it had. If you say that something should not have happened, you mean that it did happen, but that you wish it had not.

Should not have or should have not?

But "should not have" is the more natural order when you mean the same thing by both. "Should have not" is sometimes appropriate, for the same situations in which a "split infinitive" is sometimes appropriate. Also "should have" sometimes has a sort of "meta" meaning that would make "should have not" more logical.

Should not have in a sentence?

For example, You should not have believed him. You should have not to believe him.