How do I turn finished jobs into Xero invoices without billing twice?

The short answer

Keep each finished job with its evidence and the agreed price, under one job reference. Before you make an invoice, check that the same reference has not been billed. Create the invoice in Xero as a draft, check every line and tax code, then issue it. A draft lets a person catch a mistake before the customer sees it.

What to keep with each job

A job reference that never changes.
Evidence that the work was done, such as a signed job sheet, a photo or a short written note.
The agreed price or quote reference.
The Xero customer, sales account and tax code for each line.

Stop billing twice

Most double billing happens when two people bill the same job, or a job is billed again after an edit. Put the job reference on every invoice. Before you create a new one, search Xero for that reference. If it is already there, stop and check.

Why drafts first

A draft invoice is not sent. It gives a person the chance to check the lines, the price and the tax code against the job. Once it is right, you issue it from Xero in the usual way. Keep the evidence with the draft, so anyone can see why the customer is being charged.

How Completed work does it

Xevrion's Completed work needs completion evidence (a file or a written note) and the agreed price before a draft is made. It checks Xero for the same job reference, and a named person approves every line. It then creates the Xero draft with the evidence attached. Xevrion never sends the invoice: you issue it in Xero.