One small beneficiary of the investment rush into Indian internet companies two years ago was Jana, a Boston-based startup that sells ads on an app store for Indian phone users. Jana sold ad space to Indian firms like Flipkart and U.S. companies Amazon.com and Twitter, each hoping to reach Jana’s 40 million registered users. That business helped Jana raise $57 million from big names like Verizon and French ad giant Publicis last year at a valuation of between $300 million and $400 million.

But the euphoria around the Indian mobile market has faded. Mobile app developers that advertised on Jana are struggling to retain the users its ads generated. Revenue dropped significantly last year from the $30 million it generated in 2015, two people familiar with the matter said. Jana CEO Nathan Eagle declined to comment on revenue estimates.