No longer able to add payments from invoices

Let's troubleshoot the QuickBooks app on your device to restore its default settings and refresh its functionality, Paul. 
 
For Android:

1. Open Settings on your Android device.
2. Go to Apps (this may vary by device).
3. Choose the QuickBooks app from the list.
4. Tap Storage, then tap Clear data.
    

For iOS:

1. In Settings, click General.
2. From the iPhone Storage, select the QuickBooks Online app. 
3. Click Offload App. 
    

If the issue persists, I recommend reinstalling the QuickBooks app. However, if you're using an iOS device and the problem persists, I encourage you to reach out to your QuickBooks Live support team for further assistance.
 

In the meantime, you can log in to your QB Solopreneur account using a web browser on your mobile device or on your desktop to continue with your invoice task.
 

This thread is open if you have further invoicing concerns.