As a Tunisian human rights activist in the 2000s, Amira Yahyaoui staged protests and blogged about government corruption. In interviews

, she described being beaten by police. When she was 18, she said, she was kidnapped from the street, dropped off at the Algerian border and placed in exile for several years.

Ms. Yahyaoui’s compelling background helped her stand out among entrepreneurs when she moved in 2018 to San Francisco, where she founded a student aid start-up called Mos. The app hit the top of Apple’s App Store and Ms. Yahyaoui raised $56 million from high-profile investors, including Sequoia Capital, John Doerr and Steph Curry, according to PitchBook, which tracks start-ups. Mos was valued at $400 million.

In podcasts, TV interviews and other media, Ms. Yahyaoui, 39, frequently discussed Mos’s success.

Among other things, she said the start-up had helped 400,000 students get financial aid. But internal company data viewed by The New York Times showed that as of early last year, only about 30,000 customers had paid for Mos’s student aid services. The rest of the 400,000 users included anyone who had signed up for a free account and may have gotten an email about applying for student aid, two people familiar with the situation said.

After Mos expanded into online banking in September 2021, Ms. Yahyaoui told publications such as TechCrunch that the company had more than 100,000 bank accounts. But those accounts had very small amounts of money in them, according to the internal data. Less than 10 percent of Mos’s roughly 153,000 bank users had put their own money into their accounts, the data showed.

Some employees tried to speak up about Ms. Yahyaoui’s claims, said Emi Tabb, who worked at Mos in operations and had roles such as head of financial aid before resigning in late 2022. But Ms. Yahyaoui dismissed and sometimes disparaged employees who tried pushing back against her public comments, five people who witnessed the incidents said.

“She created a culture of fear,” Mx. Tabb said.

Mos is among a class of tech start-ups that rose during the fast money era of the late 2010s and early in the pandemic, when young companies landed millions of dollars in funding with little more than promises. Now as the money has dried up and many tech start-ups grapple with a downturn, investors are pickier, customers are warier of bold claims and employees are more suspicious of founder pronouncements.