Phone connection issues and computer connection issues are the two main reasons why you may not be able to send and receive messages on WhatsApp Web.
Your session on WhatsApp Web is an extension of WhatsApp on your phone. WhatsApp Web connects to your phone to sync messages, thus you can see all messages on both devices. The first requirement to being able to use WhatsApp Web is an active WhatsApp account on your smartphone.
If you cannot connect to WhatsApp on your phone to send and receive messages, then you will not be able to use WhatsApp Web. Open WhatsApp on your phone and try to send a message. If you cannot, then follow the connection troubleshooting steps for your device: Android | iPhone | Windows Phone | Nokia S40 | BlackBerry | Nokia S60 | BlackBerry 10
Once you are able to send a WhatsApp message from your phone, try using WhatsApp Web again. If you still have issues sending or receiving messages on WhatsApp Web, then there is likely a connection issue on your computer.
Note: To reduce data usage charges on your phone, we recommend connecting your phone to Wi-Fi.
Just like using WhatsApp on your phone, you must have a strong and stable Internet connection on your computer to use WhatsApp Web. If you see a yellow bar at the top of the chat list with this error message "Computer Not Connected", check to make sure your computer's Internet connection is active. If your computer Internet connection is working normally and you cannot send or receive a message on WhatsApp Web, first refresh the page.
If the problem persists, you should log out and log back in to reactivate your web session:
Menu icon.Important: You must use the latest version of Chrome, Firefox, Opera or Safari as a web browser to use WhatsApp Web. Other browsers such as Internet Explorer are not supported.
If you use WhatsApp Web on a managed Wi-Fi network, such as at your office or university campus, your network might be configured to block or limit connections to WhatsApp Web. If WhatsApp Web notified you that you’re on a Wi-Fi network that is preventing WhatsApp Web from operating correctly, please ask your network administrator to bypass traffic to web.whatsapp.com and *.whatsapp.net.
Cheers,
WhatsApp Support Team