[gregjor]

For my own clients I use a spreadsheet in Google Sheets to track my work, either time or tasks and deliverables. I generate invoices from that, as PDF files, then send those by email to whomever approves and pays. I can give clients access to the spreadsheets if they want that.

I work through an agency that has its own work tracking also in a spreadsheet. They handle invoicing and collecting payment for their customers I work with.