Please follow these steps on your Android device if you are getting above error.
Update device OS if available.
Update Google Play Store App. Refer https://support.google.com/googleplay/answer/113412?hl=env
After you update Google Play Store App as per above link:
Go to Settings -> Apps –> Select Google Play Store App.
“Clear Data Storage” of the Google Play Store App.
Then “Force Stop” Google Play Store App.
Now open Google Play Store App.
Kill iPlum app if it is already in recent apps.
Open iPlum app and try again.