Sales | New Invoice - Only show Customers when entering Contact
When creating a new invoice, the search scope includes every contact in the database, every vendor, evert coffee shop or gas station anyone ever used a credit card at. Xero knows which contacts are Customers (there's a Customer Invoice report), it should pull from Customers only. For the use case where someone is invoicing someone for the first time, they can open that Contact and then click New Invoice.

Appreciate you sharing your feedback with us here, Rob. Understand how this could help you find the contact you're after if your supplier and customer lists are quite separated.
We'll get a sense of others that would also like to see this from your idea here. If there are any updates we'll let you know.