Since yesterday afternoon I am unable to launch my WhatsApp on Lumia 640. I tried reinstalling and even factory reset the phone but it's not opening. Please help me fix it.
Try these steps to fix your connection. They're from the WhatsApp FAQ and are written for Android, but the basic steps should apply to Windows phones as well.
- Restart your phone, or turn it off and on.
- Update WhatsApp to the latest version available on Google Play.
- Open your phone's Settings app > More > and turn Airplane mode on and off.
- Open your phone's Settings app > Data usage > and make sure that Cellular data is turned on
Make sure that your time and date of your phone is correct.