In the manual it says the following…
When creating a invoice, start typing the name of the client to create the invoice for. If it’s an existing client, choose their name from the list that appears. If it’s a new client, type their full name or business name. Choose the date and invoice group and press the Submit button.
I couldn’t figure out how to Create Invoice from here by “type their full name or business name” without “Add Client” first.