How do I show "hidden items" in my reimbursable items group when I bill a customer?

Hello, jstone. 

Thank you for reaching out to the Community. I understand you want to show the reimbursable items grouped into one line item amount in QuickBooks Online. Unfortunately, it's not possible to show the grouped line item amount in the invoice once you send it to your customer. But don't worry, our team is continuously working to improve our services and add more features for our users. We highly value your suggestions and encourage you to send us your feedback. All your ideas will be carefully evaluated and considered for inclusion in our future product developments. So, please share your thoughts with us. We appreciate your valuable input.

To submit feedback for QuickBooks Online, here's how: 

1. Go to the Gear icon and select Feedback.
2. Provide your product suggestion.
3. Click on Next to submit feedback.

I've added an article for your future reference about receiving payment and recording it: Record invoice payments in QuickBooks Online. 

Please feel free to reach out if you have any further questions or need additional assistance. We are here to help you. Have a great day!