We can look into your preferences and perform a few troubleshooting steps, megschlegel.

Let's check your preferences to see if options are enabled for pop-ups to show. Let me show you how:

1. Go to the Edit menu and select Preferences. 
2. From the left menu, click General and then My Preferences.
3. Check the Bring back all one time messages box. 
4. Click OK. 

Then, let's update QuickBooks to its latest release to have up-to-date fixes and features. Then, verify and rebuild the data can also help us resolve data damage within the company file. After that, you can close and reopen QuickBooks and recreate an invoice to check if the Billable expense window now prompts. 

I'll be attaching an article that will help manage your billable expenses: Tracking job costs in QuickBooks Desktop

I'm just around if you need more help. You take care always!