WhatsApp reportedly has been conducting tests of a business chat system with a number of companies that are part of the Y Combinator startup incubator. The application programming interface, or API, gives companies a direct line of communication with WhatsApp users. WhatsApp CEO Jan Koum last year said the company would seek to monetize the free chat service by providing businesses with direct access to consumers. He ruled out ads. The approach WhatsApp is taking could have stumbling blocks built in.