Slack Invoice

Inspiration

Teams live in Slack, but invoicing still means switching to Stripe — a founder billing after a DM, a freelancer invoicing from a project channel, finance checking if a client paid. SlackInvoice brings billing into the chat, inspired by the Slack Agent Builder Challenge and built with MCP (Model Context Protocol) so Stripe logic is a reusable service, not locked inside one bot.

What it does

DM or @mention SlackInvoice in plain English:

"show me all customers"
"invoice Acme Corp, ap@acme.com, for $1,500 — Q1 consulting" (company name, email, amount, and description for new customers)
"show open invoices" / "how much have we collected?"

It returns natural Slack replies with invoice IDs and payable Stripe links (test mode). New users get a welcome intro on first open; in-thread progress updates while the agent works.

How we built it

Slack bot (Bolt, Socket Mode) → LangChain + Groq (classify → parse → format) → MCP client → FastMCP server (8 Stripe tools) → Stripe test API.

Two processes on one Linux VM; bot uses MCP_URL=http://127.0.0.1:8000/mcp. No public inbound ports — Socket Mode connects outbound to Slack.

Challenges we ran into

Stripe invoices need line items attached to a specific draft invoice before finalize
NL parsing must map "3 hours at $150" → structured fields (Pydantic + prompts)
Cross-platform deps (pywin32 in a Windows pip freeze broke Linux installs)
Slack Bolt handler wiring — handlers had to register on the real app instance
Scope: focused on create, list, status, search, void, revenue — not a full billing suite

Accomplishments that we're proud of

Full create → finalize → payment link flow from a Slack message
Reusable MCP server testable without Slack (test_tools.py, test_nl.py)
Socket Mode demo on a single VM — simple for judges to run
Open source: github.com/zhuwensh/slack-invoice

Track: New Slack Agent · Tech: MCP server integration

What we learned

MCP cleanly separates UX from billing APIs. A classify → parse → format pipeline kept billing actions reliable while replies still feel conversational. Socket Mode is ideal for hackathon demos. Stripe’s invoicing API has non-obvious edges worth reading the docs for.

What's next for Slack Invoice

Let teams deploy their own SlackInvoice instance with their Stripe and LLM API keys — billing stays in their account while the agent stays in Slack.
Add support for PayPal and other billing platforms via additional MCP servers, so Slack remains the interface regardless of payment provider.