Ref: Pizza Video Tutorial 3
https://www.youtube.com/watch?v=40aWH3Gqn28
After setting up the invoice table's fast form, the part where the Customer is looked up is missing.
Even after manually doing all the steps, I see that the customer_id is being displayed and something is amiss in the invoice form as well where the lookedup value is shown in the right and the customer-id is being displayed!