Where can i fine the novel

It most likely not based on novel, but inspired by real youtube idol group by the same name: Millionaire.
Their characters names and personalities all the same in youtube and in webtoon.
The group start first before the webtoon came into existence.
When the webtoon start, the group also promoted them in their youtube official.

You can search youtube: Millionaire Official.

I totally recommend checking them out. Their voice and personality is exactly jow I imagine them would be when I read the webtoon.
My favorite is definitely Si-Yoon. He got that confidence, easygoing, but calm leader like voice.