There are several reasons why you can not send or receive messages in WhatsApp Messenger, the most frequent is a bad connection to the Internet. But, if you already proved that you can connect to the Internet with other applications, then there may be other causes.
Causes why you can not send or receive messages in WhatsApp if there is a good Internet connection
The person to whom you sent the message blocked you or your number is wrongly registered in your contact list. Also, you may not have completed the initial verification process or changed the SIM card. WhatsApp works only with the phone number you have registered.
Possible solutions for resending and receiving messages in WhatsApp Messenger
To solve the problem try restarting your mobile device: turn it off, wait about 30 seconds, and turn it on again. Also, make sure your contact number is correct and that the SIM card is inserted correctly.
Perhaps in your country, it is blocked
In some countries using this app is prohibited. In Dubai, for example, text messages are working but video calls or calls are not as it is blocked.