Thanks for informing us how the troubleshooting wen through, HAM9000.

In this case, our customer support will take a closer look at this to determine why the Invoice tab is missing. 

Here's how you can reach out to them:

1. Click the Help menu and click Contact Us.
2. Let them know that the Invoice tab is missing in the Sales menu, then click Let's talk.
3. Click Chat or Email us.

Please take note that our Chat Support Team is open from Monday to Friday, in between 9 AM to 6 PM (GMT +8). 

Visit us again in the Community if you need anything else.