Im trying to enter invoices and forward date to our correct delivery day, but the app wont let me change the date.

Hello there, @tdff.

Thank you for posting here in the Community. I want to make sure that you can edit the invoice date in your QuickBooks Self-Employed (QBSE) account without any error. 

There are two options on how to resolve this error depending on the device you're using:

• Reset app data to start a clean slate.
• Uninstall and Reinstall to refresh the system

First is to reset the app, here's how using the android device: 

1. Go to your phone Settings. 
2. Tap Apps and Notifications.
3. Look for the QuickBooks Self-Employed app.
4. Select Reset App Data.

Using iOs:

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

The second option is to uninstall and reinstall the app. For uninstalling the QBO app using iOs device, you can touch and hold the app, then click the Delete app button. Nothing to worry about uninstalling the app because it won't delete the subscription you have. 

For android: 

1. Tap Settings on your phone.
2. Select Apps and Notifications, then locate the QBSE app.
3. Hit Uninstall. 

After that, reinstall the app by going to this link: https://quickbooks.intuit.com/accounting/mobile/.

You can also log in to the web and change the invoice date from there. 

To receive an invoice payment using the QuickBooks Online mobile app, just click this article: Receive an invoice payment using the QuickBooks Online app

Stay in touch with me if you have any other questions. I'm always happy to help. Take good care.