I appreciate you reaching out here in the Community for support. I want to make sure you're able to create an invoice.
If certain buttons aren't working, or things aren't displaying as they should, this can mean the cache is full in the internet browser. This can be fixed by clearing it. Clearing the cache forces QuickBooks Online to refresh and allows you to work with a clean slate. For example, if you're using Chrome, here's how you'd get this done:
1. Click the three vertical dots in the top right corner.
2. Select History, then History once more.
3. Choose Clear browsing data.
4. Change the time range to All time.
5. Click Clear data.
This article provides similar steps for different browsers: https://quickbooks.intuit.com/community/Getting-Started/How-do-I-clear-my-browser-cache-and-temporar....
Let me know how things look after giving this a try. I'll be here if you have any other questions.