"Whats" isn't a generic term in the computing field. "WhatsAPI" isn't a dictionary word, it's a colocation of Whats and API, the first element being chosen specifically to render association with WhatsApp. The use of WhatsAPI differs in only one letter from the trademark.
IMO provided they headline the fact they're not associated nor extraordinarily authorised by WhatsApp then there would be no actual trademark issue; the law I suspect will see it quite differently.
"Whats" isn't a generic term in the computing field. "WhatsAPI" isn't a dictionary word, it's a colocation of Whats and API, the first element being chosen specifically to render association with WhatsApp. The use of WhatsAPI differs in only one letter from the trademark.
IMO provided they headline the fact they're not associated nor extraordinarily authorised by WhatsApp then there would be no actual trademark issue; the law I suspect will see it quite differently.