Why is What'sApp acting up?

[AC Question]

Whenever I try to sign up on my Android Optimus 90, What'sApp doesn't accept my phone number saying that my phone number is invalid to the country United States. This is getting really annoying. Please help me fix this problem of mine!

 

[Golfdriver97]

Welcome to Android Central. Have you tried uninstalling and reinstalling WhatsApp?