Affiniti founders Aaron Bai, 20, and Sahil Phadnis, 22, are building a fee management software for the small businesses on the main street that technology startups have enjoyed for years.

Their growth was so impressive that six months after raising $11 million in seed rounds, they raised $17 million in Series A, led by Signal Fire, who specifically told TechCrunch.

Affiniti offers small and medium-sized businesses such as Pharmakies, HVAC companies and car dealers, customizable fee management credit cards, and software similar to merchandise pioneered by Brex and Ramp.

However, traditional small businesses already have credit card options from companies such as American Express and Capital One, as well as traditional banks. Why did they choose affiniti?

Because, Bai said, the startup is offering what he calls the fintech “V3.” He believes that Section 1 is traditional banks and credit cards. BREX and RAMP stand for V2, which brings improved UX design and better access to the financial data generated by the expense.

“V3 is a fintech product that can actually advise end users and provide them with analysis,” Bai said. “These traditional small businesses don’t have financial teams.”

Series A cash will help launch launch release features such as bank payments, cash flow analysis, and integration with enterprise resource planning and point-of-sale applications.

Currently, it offers features such as custom cash rewards, native QuickBooks "QBO" files (not just CSV files), and short-term loans for invoices up to 90 days.

Interestingly, unlike many founders in their 20s, Affiniti is not from an entrepreneurial school like Y Combinator. The founders said they didn't have to. They met while attending UC Berkeley, which helped them build a solid network in Silicon Valley to introduce VCS and others. They said they also proposed their own marketing campaigns, working with specific industry trade groups, such as independent pharmacies.

Not only does this help validate the startup to potential customers, it also gives them immediate access to features like collective purchase discounts. “In fact, when working with every SMB in the U.S., we’re not going to boil the ocean,” Phadnis said. “We’re choosing some niche verticals with complex cash flows.”

All of this is good enough to get Affiniti from zero to 1,800 customers and about $20 million in monthly transaction volumes in the first 14 months, Phadnis said. The founders believe that by the end of this year, the platform can reach $1 billion worth of deals.

As the startup makes most of its money on transaction exchange fees, although it also sells SaaS software and earns interest income on these short-term loans, it means revenues grow rapidly.

Although the founders won’t disclose their current income, Fadney offers a tip for your career: income grows about 10 times over the year. "Twelve months ago, we were priced at one million dollars. So 10 times a lot," he said with a smile.

Other investors in the Series A Series include Codie Sanchez’s Counter-Trend Thinking Capital, Yahya Mokhtarzada (founder of Truebill) and Austin Rief (founder of Morning Brew).

Seed Investor Indicators Ventures, Lampshade Ventures and Riverpark Ventures also attended the conference. It said Affiniti also signed $15 million in debt institutions, able to grow to $50 million, its earlier seed round.