Try the following steps to workaround this issue:
- Quit App Store.
- Wait 10 seconds or more.
- Open App Store again.
- Navigate to the desired app.
- Click Buy.
If the issue persists, try restarting your computer and attempting the app purchase again.
Learn more
- For other solutions to App Store issues, see Troubleshooting the Mac App Store.
- You can find additional information by choosing Help > App Store Help from within the application.
- Additional articles and support resources for Mac App Store are available from the Apple Support Website.