I'm here to help you with the invoice dates, devloo.

QuickBooks Online uses the device/computer's date when creating a transaction, including invoices and payments. We have to make sure that the device/computer has a correct time and date. You'll want to edit it if needed. If it's in the right date format, we can troubleshoot your browser to see if this is the reason of this behavior. We can open an incognito, then create and save the invoices from there. The same goes with the payment transactions. 

I also suggest clearing the cache. It is a junk file that the browser saves and it causes error in QuickBooks Online. Aside from that, make sure that your browser is updated. You can also use another one like Google Chrome, Mozilla Firefox, or Microsoft Edge.

I'd like to share the new invoicing feature in QuickBooks Online. This helps so you'll get paid faster within QuickBooks.

I'm just a post away if you need further assistance. Wishing you all the best!