First, ensure a solid Wi-Fi signal or mobile data connection. Video calls demand more bandwidth than texts or voice calls, so you can't expect the feature to work properly with a weak connection. On top of that, we would recommend switching between Wi-Fi and cellular to see if one works better.

Keeping your WhatsApp application up-to-date is the key to a smooth flow of operations. Using an outdated app will cause issues such as slow performance and different features, such as video calls, not working properly. So, head over to the Google Play Store or Apple's Play Store, search for WhatsApp, and download the latest update from there. 

WhatsApp requires you to give it certain permissions to work properly. If you're facing the WhatsApp video call problem, it may be because the app does not have access to your camera and microphone. 

To resolve this, follow these steps:

• Go to your phone's settings.
• Access applications.
• Tap on WhatsApp.
• Go to Permissions.
• Give it access to your camera and microphone. 

Old cached data can get corrupted at some point, which can cause different performance issues. To fix this, you need to head over to your phone's settings, make your way into “Storage,” and tap on “Clear Cache.” This won't delete your data, but it will get rid of the corrupt cache files and improve the overall performance of your device. 

If you have the power saving mode enabled, it may be causing the WhatsApp video call problem. Power saving can help save the battery, but it will also restrict background apps and prevent them from working at their full potential. So, go back to your battery optimizations settings, disable the power saving mode, and try video calling through WhatsApp again. 

If you’re continuously facing the video call problem, it may be because there’s a virus on your device. If you recently downloading something from an untrusted site or source, you need to use an Antivirus to scan your device and eliminate all viruses that may have made their way into your device.