Best Friends with the Billionaire by Liwen Y. Ho

He’s a down-to-earth tech guy. She’s his boss’s billionaire sister. A flirty relationship moves beyond the friend zone during a tropical getaway.
Noah Carter wants nothing more than to impress his best friend’s sister. He may not have money to whisk her away to Paris, but he’ll do anything to support her. He jumps at the chance to spend a day by her side on a shopping spree, but hates being reminded of all the things he can’t provide for her.
Laurene Brooks doesn’t let any price tag stand in her way of getting what she wants. But the one thing she longs for—her brother’s best friend—can’t be bought. That doesn’t stop her from blurring the lines of friendship and having a little fun.
As different as their backgrounds may be, this unlikely couple soon discover a common denominator in love.