Ask a freelancer about cash-flow problems and they'll tell you about late-paying clients. Real problem. But there's a quieter, more expensive one almost nobody tracks: the work you finished and never invoiced. The extra revision you did on Friday. The "quick favor" that took two hours. The milestone you completed but forgot to bill because you were already deep in the next project. None of it is "late", it's just invisible . And invisible work is unpaid work. Why it happens Invoicing is a contex