Invoices are usually raised in whichever system holds the job — your field service system if one is connected, or directly here.
Raising one here
Go to Operations, then Jobs, and open the job the work belongs to. Its Invoices tab has a New invoice form: add a line for each thing being charged, with a description and a rate, and create it.
An invoice is raised against a job rather than on its own, because that is what ties what you charged to what the work cost — see job margin. If QuickBooks is connected the invoice syncs across, so it does not need entering twice.
Billing that does not belong to a job is raised at Accounting, then Invoices, which is also where payments, credit notes and the receivables aging live — see raising invoices.
Operations, then Invoices lists everything raised. Accounting, then Receivables & Payables shows what is still outstanding and how far overdue it is; that view reports rather than creates.
The three things that decide when you get paid
Not persuasion. Process.
Invoice the day the work finishes. Month-end invoicing adds up to four weeks to every job before the customer has done anything at all. This alone is often a fortnight of days to get paid.
Send it to the person who pays, not the person who booked the work. In anything commercial these are different people, and an invoice sitting with the wrong one is the most common silent delay. Ask for the accounts contact and any purchase-order number before you start — see purchase orders.
Include a way to pay it. An invoice a customer can pay from their phone gets paid in days rather than weeks. See invoicing setup.
Getting the details right first time
A wrong address, a missing reference, an unclear description — each of these sends the invoice into a query queue, and larger customers will not chase you for the correction.
Terms
Say them on the quote rather than introducing them at the invoice, where they read as a surprise. See payment terms.
After it is sent
Reminders can go out on a schedule rather than when somebody works up to it, which is most of why they work — see collections.