There are many reasons for not receiving WhatsApp messages, as follows:
The phone may be out of coverage area.
This person may have blocked you.
The other person's phone may be off.
There may be a problem with WhatsApp itself or the mobile network.
There are a lot of WhatsApp cache files.
After you determine the cause of the problem, here are some suggested solutions:
First, check the speed of your Internet connection
Restart your device and then... WhatsApp update from Google Play Store
Reset network settings on your phone
Check the WhatsApp server
Make sure to grant WhatsApp all permissions from your phone's Settings app > Apps > WhatsApp > Permissions.
Turn on airplane mode on the phone for 60 seconds, then exit airplane mode and try using WhatsApp again
Clear the cache on your phone