To reduce invoice entry mistakes in the app:

1. Open Customers and complete the billing email, address, VAT number, and default payment terms for the customer
2. Reuse that saved customer record when creating the invoice instead of retyping the details
3. Preview the invoice before sending so you can verify the saved customer data, line items, and PDF layout
4. If the wrong data keeps appearing, update the customer record or company settings first, then create or refresh the draft invoice