The Kissing Booth is based on a fanfic. It's not a completely original concept. The fanfic's popularity might have led to its transformation into a more mainstream form of entertainment.
The Kissing Booth is not based on a true story. It was a creation that started in the world of fanfiction. Fanfictions are fictional works written by fans, often inspired by other existing works, but not based on real - life events. In the case of The Kissing Booth, it was the imagination of the author Beth Reekles that brought the story to life, and then it was developed further for the screen, but there is no real - life basis for the story.
Yes, 'The Kissing Booth' was originally a Wattpad fanfiction. It gained a lot of popularity on the platform before being adapted into other forms like a movie.