App not working to create invoices. States Call succeed but payload is empty

We can perform troubleshooting steps to help fix the issue in your mobile app.

If the application is experiencing functionality issues, it is advisable to clear its cache files. This action serves as a beneficial preliminary measure to address various errors.

Follow these steps if you're using an iOS device: 

1. Select the menu at the top right and then choose Help & Feedback. 
2. Click Refresh Data and Refresh. 

For Android devices: 

1. Select the menu at the top right and choose Settings. 
2. Press Refresh Data and choose Yes.

To access the necessary settings on your Android phone, navigate to the Apps section, which may differ depending on your device. Locate the QuickBooks app within the list and select Storage. Finally, choose the option to clear data.

To manage the storage on iOS, access the Settings menu on your device, then navigate to General and select iPhone Storage. Identify an application that occupies a significant amount of space. You can free up the storage without removing the app's documents and data by opting for the Offload App feature.

Once done, restart your mobile phone and verify whether you can utilize your mobile application to create invoices.

If the problem continues, please consider uninstalling and then reinstalling the QuickBooks Online mobile application.

I'm adding this article for reference and to learn more about the QuickBooks app: Mobile app FAQs.

You can comment below for any follow-up questions regarding the mobile application. I am always available to assist you. Best regards!