If you have not received invoice automatically, via email, after your trip was booked and ticketed, you can try the following
check your itinerary for phone or email credentials and contact your Booking/Travel team directly
access myCWT website, open your trip for which you need the invoice and click on Download button (this will download your Itinerary which in some cases can be used as invoice). Please note Download is not available to all clients so this is possible the button does not work for you.