Start creating an invoice with the app you have created so far. To create that invoice, you will have to select a Customer for it. Currenty, your app will have a “Prompt” interface associated to the CustomerId field to help you choose the customer you want.
In your KB, this interface was created automatically by GeneXus. You can improve it using K2BPrompt pattern. The following exercises will guide you in applying this pattern and customizing the result.