Central to Spotify's complaint, filed to the European Commission on Monday, is what it says is a 30 percent fee Apple charges content-based service providers to use Apple's in-app purchase system (IAP). Horacio Gutierrez, Spotify's general counsel, said the company was pressured into using the billing system in 2014, but then was forced to raise the monthly fee of its premium service from 9.99 to 12.99 euros, just as Apple Music launched at Spotify's initial 9.99 price. Spotify then ceased use of Apple's IAP system, meaning Spotify customers could only upgrade to the fee-based package indirectly, such as on a laptop. Under App store rules, Spotify said, content-based apps could not include buttons or external links to pages with production information, discounts or promotions and faced difficulties fixing bugs. Such restrictions do not apply to Android phones, it said. "Promotions are essential to our business. This is how we convert our free customers to premium," Gutierrez said.