Error code 491 on my tablet ZTE K88

Try this steps ... https://www.errorcodeexpert.com/how-to-fix-google-play-error-code-491/

Clear Cache and Data in Google Play Store App:
This should be done from the System Settings by ust following the steps given below. Make sure that before you go and do this step you have to Turn off Google play updates from the Play Store app. Open Paly Store and tap on the 3 dots option icon on the right or left side top of the screena nd from the list of options turn it off.

1. Go to System Settings on your android device which is Gear shaped icon -> Tap on Application Manager or Apps in the list of options -> Then Open "All" apps
2. From the List of Apps available in the All apps search for the Google Play Store App and Tap on it which will open a new window.
3. You should click on the Clear Cache button and Clear Data button as shown in the image below.
4. Now Restart or reboot your device and try to install or update the apps which will most probably solve the problem. If you are still facing the same error and problem follow the next step.