Not true. They were charging 1€ a year, not a month (at least that's the case in my country). The math doesn't add up.

Kinda surprised the parent made such a mistake since Whatsapp was very well known in tech circles for charging an incredibly low fee pre-FB acquisition. And the parent's HN account dates from 2010...

My bad, it was of course per year. Point still stands that $1/year was a viable business model that covered their burn rate and then some.

They probably got initial funding from investors thinking about a future exit. Investors aren't as interested in a company that intends to simply survive on modest profits forever. This is also why startups tend to magically die when big companies aren't doing well.