Why does Malvolio fall for the prank?

I'm sorry, additional information is required in order to answer your question. Act? Scene?

Though he is a character who can not be played around with,Malvolio falls for a not-so-well-planed prank firstly because of his desire of power ( clear through his verbal-jugglery ) which ,he thinks, will come to him only through the marriage with olivia and also shakespeare wanted to mock the tendencies of Puritans of that age,so in this scene he is designed by the author to fall for this prank.

Because he is in love with Olivia