Went onto my app today and no invoices are showing or customers or anything?

A warm welcome in the Community space, wildflower. 

Let's take some time to troubleshoot and resolve the unusual behavior exhibited by the application. The app's data may have reached its capacity, which can lead to certain functions not working as intended.

For iOS:

1. Go to the Help menu.
2. Select Reset App Data.
3. Click on OK.

For Android:

1. Proceed to the Home menu or tap the three dots in the right upper right corner.
2. Tap on Settings.
3. Select Refresh Data.
4. Click on Yes.

If the problem persists, please uninstall and reinstall the application. In the meantime, you can open your account using your web browser to access your invoices. 

Additionally, you can refer to this article about making quick changes to invoice templates while you're on the go: Customise invoices on the QuickBooks Online mobile app.

Let me know if you need further assistance managing your invoices within the app. I'll be here to help you.