I built and shipped a SaaS in one day — here's exactly what I used

PayFlow — Fri, 26 Jun 2026 12:26:05 +0000

I woke up this morning with no idea what to build. By the end of the day I had a live SaaS product with auth, a database, automated emails, a custom domain, and a real paying-customer pricing model.
Here's exactly what I built and how.
The problem I picked
After researching complaints on Reddit and G2, one pain point kept coming up: freelancers hate chasing late invoices. Not because they don't know how — because asking for money feels awkward. So they delay it. And lose thousands every year.
The solution: automate the whole thing.
What I built
PayFlow — it automatically sends follow-up emails when invoices go overdue. Friendly reminder at day 7, firmer follow-up at day 14, final notice at day 21. It also shows which clients pay slowest so you know who's worth keeping.
Live at: usepayflow.com
The stack

Next.js 15 (App Router) — fullstack, one repo
Supabase — auth + Postgres database in minutes
Resend — transactional email API for the chase sequences
Vercel — deployed in one command, cron jobs built in
Cloudflare — domain registered and DNS managed

What took the longest
Honestly? The landing page copy. The code was fast. Finding the right words to explain the problem took longer than building the solution.
What's next
Getting real users. Everything else is noise until someone pays for it.
If you freelance and deal with late payments — try it free at usepayflow.com. I'd love your feedback.

DEV Community: PayFlow

I built and shipped a SaaS in one day — here's exactly what I used