Whatsapp is fully functioning for myself, it did take about 3 seconds to verify my number.

However, if you're unlucky and Whatsapp does NOT work for you, I found a method that is supposed to work :

send SMS to +44 7900 347295

NOTE. THE +44 IS THE CODE FOR THE UNITED KINGDOM. (UK)

that should verify your number, if you are in a different country, try your countries code but I'm not too sure about if that will work or not.