Meaning of “make sth up” - Learner’s Dictionary

make sth up

phrasal verb with make us uk /meɪk/ verb [ T ] past tense and past participle made

B2 to say or write something that is not true:

I made up some story about having to go and see my sick mother.

(Definition of “make sth up” from the Cambridge Learner’s Dictionary © Cambridge University Press)