Yaniv Liron has pulled cash and credit from every available source to keep his 11-year-old web design and development business, Lumina, running smoothly — a situation familiar to many small-business owners.

Even though his company, in New York City, is established and profitable, obtaining a bank loan or credit line has always been painful. The paperwork takes days to prepare, approval decisions can drag on for weeks or months and the process, he said, “involves selling your soul and begging on your knees.”

Four months ago, he found a simpler source of working capital: Fundbox, a company that gives business owners cash advances against their outstanding invoices. Within an hour of signing up on Fundbox’s website and allowing access to his company’s bank account and accounting software, QuickBooks Online, Mr. Liron had a $2,500 credit line. It takes just a few mouse clicks for Mr. Liron to select an unpaid invoice in QuickBooks and have Fundbox rapidly deposit the cash into his bank account.