Using ServiceTrade and QuickBooks together, you can give your operations team (schedulers, technicians, etc) real-time visibility into job costs, AND make sure that the accounting controls that your business requires are being followed when you have to purchase materials to perform a job.
Normally, ServiceTrade will create customer and job records in QuickBooks at the end of a job's lifecycle, when you send an invoice from ServiceTrade to QuickBooks. However, if you need to use purchase orders to authorize parts purchases, you will need the job to be in QuickBooks earlier, before it's invoiced -- probably even before your technician arrives onsite -- so you can associate purchase orders with that job.
Please note that you'll need to use the "Customer: Job" or "Customer: Location: Job" mapping for QuickBooks. See the "Customer mapping" section of this article for more information about how to set up your customer mappings. You'll also need to be using a version of QuickBooks Desktop that supports inventory management (this is required for you to make use of purchase orders). QuickBooks Online does not officially support job costing.
To send a job from ServiceTrade to QuickBooks, click the "Send" button at the top of the job page, then choose the desired QuickBooks Desktop connection from the list that appears. Just like with invoices, the job will appear in QuickBooks once your QuickBooks Web Connector has synced all new changes from ServiceTrade to QuickBooks.
Once the job is created in QuickBooks, you can create purchase orders against it. When the job is eventually invoiced in ServiceTrade and the invoice is sent to QuickBooks, that invoice will be associated with the same job, so you'll be able to create gross margin and profitability reports that make use of the job-level cost and revenue information that you've tracked.
Only the empty job is created in QuickBooks Desktop when synced. No Job items, comments, services, or other jobs contents are passed over.
For more information about job costing in QuickBooks Desktop, this QuickBooks help article has a great introduction.