The idea
A lightweight web app that connects to your invoicing tool (or just accepts a CSV/API push) and tracks each invoice's due date and payment status. As invoices age past due, it drafts follow-up emails with escalating tone, from a friendly nudge on day 3 to a firmer note on day 21, and queues them for one-click send. It doesn't replace your invoicing software, just the manual, dreaded part: remembering to chase people and figuring out how to word it.
Why build this
Freelancers and small agencies lose real money to late payments, but chasing clients feels socially awkward, so people put it off, which makes it worse. Most invoicing tools (FreshBooks, Wave, Stripe Invoicing) send one generic reminder and stop. LLMs are now good enough to draft context-aware, appropriately-toned emails cheaply, and freelancers already trust AI-drafted communication for client-facing writing. This is a narrow, unsexy problem with real willingness to pay because it's directly tied to cash flow.
Stack sketch
- Frontend: Next.js, Tailwind, a simple dashboard listing invoices with status and next scheduled follow-up
- Backend: FastAPI or a Next.js API layer, Postgres for invoices/clients/follow-up history
- Email sending: Resend or Postmark, with reply tracking via a unique thread header so payment confirmations or "already paid" replies pause the sequence
- AI drafting: Claude API, prompted with invoice amount, days overdue, past correspondence tone, and client name, to generate 2-3 draft variants per escalation stage
- Integrations: Stripe and PayPal webhooks to auto-mark invoices paid; a CSV import and a simple REST API for tools without webhooks
- Scheduling: a cron worker (or n8n) that checks invoice ages daily and enqueues drafts
Scope for v1
- Manual invoice entry plus CSV import (skip deep integrations with every invoicing tool at launch)
- Three escalation stages: gentle reminder, direct follow-up, final notice, each with an AI-drafted email the user approves before sending
- Stripe payment link auto-detection so "mark paid" happens without user action when possible
- Dashboard showing outstanding total, days overdue, and next action per invoice
- Out of scope for v1: multi-currency, team/multi-user accounts, native invoice creation (generating invoices), phone/SMS reminders
Where it could go
The natural next step is bidirectional integration with QuickBooks, Xero, and FreshBooks so invoices sync automatically instead of being pasted in, which removes the last manual step and turns this into a background service. From there, a "client trust score" that tracks average days-to-pay per client could help freelancers decide who to require deposits from before starting new work. Longer term, auto-send (not just draft-and-approve) for trusted low-risk clients would remove the human loop entirely for the easy cases.
Watch out for
Tone control is the whole product here: an email that reads as too aggressive can damage a client relationship worth far more than the invoice, so the AI drafts need conservative defaults and an easy edit step before every send, never fully autonomous sending in v1.