So you've made an Invoice and sent it to your traveler, and they've responded. Great!
To find the response, just follow the steps below.
1. Click on the Trip
Click on the Trip that has that Supplier Invoice.
2. Click on the Invoice
In the list of items on the left, you'll find the Supplier Invoice under itineraries and proposals in Forms & Other:
3. Click on Authorizations
After you've opened the Supplier Invoice, click on the Authorizations tab:
From there you will see which charge was authorized, you can view the card information they submitted, and you can mark the payment as paid!