Hello there, wjurls. I understand you're having issues creating an invoice without entering sales tax. I'm here to provide some troubleshooting steps.

Since you cleared the cache, I suggest an alternative approach to refresh your data. You can try to uninstall and reinstall the app to resolve any unexpected behavior. Also, make sure to download any updated security settings. 

If the issue persists, I recommend contacting our QuickBooks Online Support team. They can create a ticket for further investigation and help you resolve the issue.

Also, I suggest checking out this article to help you enumerate the features supported by each device: Compare mobile app features.

Please feel free to post here again if you have any other concerns about creating your invoice. I'm always here to provide further assistance. Have a great day.