FastPay, a startup that’s all about the Benjamins, has just wrapped a $25 million round to keep the money flowing (and the lights on) around the Internet.

What FastPay does is interesting: It provides cashflow for online startups that rely on advertising money from big brands, most of which have very long payment cycles.

When you’re a lean, mean, hungry startup waiting a few months to get your first big check from Nike or Procter & Gamble, having funds when you need them is key — especially if you’re bootstrapped. Since most brands take around two months to pay their online advertising invoices, FastPay steps in with credit lines up to $5 million for a range of online businesses, including web-based publishers, digital creative studios, and ad-tech businesses.

FastPay typically lends its customers between $100,000 and $3 million, and the majority of its requests for loans are fulfilled within 24 hours.

“FastPay has been a lifesaver for us, literally,” said David Segura, CEO and founder of Giant Media, in a release this morning. “We feel very fortunate to have a partner that understands our business and is willing to underwrite and accelerate our growth.”

Today’s $25 million funding was provided by Wells Fargo Capital Finance and a subordinated debt and equity investment from SF Capital Group (don’t be fooled by the name; this firm is based in New York City). As part of the deal, SF Capital Group President Neil Wolfson and Howard Capital Management Managing Partner Jason Kaplan will join the FastPay board of directors.

FastPay is based in Los Angeles, Calif., and was founded in 2009. The company raised a previous $5 million funding round in February 2011, bringing its total raised to $30 million.