How do I send an invoice?

Three steps: the customer (type a name and a new customer is saved as you go), the line items (your saved prices are one tap away, or type a description and an amount), then review and Create & email (the button reads Create & share link when the customer has no email address on file). The email carries the total, the line items and, when Stripe is connected, a Pay button. Default terms, the late fee, the tax rate and tips are set on Get Paid's own Settings tab (Invoices) rather than in the business Settings, and each invoice can override them.