Black Survival's Ad revival system is using a program called Unity AD.
Video ads in this Unity AD have a fixed number of ads available per day.
If you watched video ads in other game than Black Survival, you may have used the number of times that Unity AD program has set up.
If so, you may not be able to revive your character by pressing the Ads revive button of Black Survival.
If this is not the case, check your device's operating system and follow the steps below.

1. Device settings-Application manager-Black survival-Storage-Clear data/cache file
and reboot your device.
2. If the problem is not resolved, go to device settings-Google-Ads-Reset advertising ID-OK
and reboot your device.

Settings-Privacy-Advertising-Reset Advertising Identifier-Reset
and Reboot the device

If the problem is not resolved, please ask us via game report!