Invoicing you can script, subscribe to, and hand to an agent
A REST API for invoices, clients and remittance advice, signed webhooks for the events that matter, and an MCP server for your AI client. API keys, the REST API and the MCP server are included on the Professional plan and above.
01 / API & Webhooks
What is the Invoice My Clients API?
The API is the programmable side of your account. With a Bearer key you can list invoices and clients, create draft invoices and clients, manage remittance advice, and trigger an e-invoice send, from your own code, Zapier or Make. Outbound webhooks push events to your endpoint the moment something changes.
The same key connects the MCP server, so Claude, an IDE or any Model Context Protocol client can use the tools the in-app assistant uses: invoices, clients, payments, proposals, time tracking, reports and more. Keys are created under Settings, then Developer, on the Professional plan and above. Free and Starter accounts have no API or MCP access of any kind.
- Professional plan and above: API keys, the REST API and the MCP server.
- REST v1 endpoints for invoices, clients and remittance advice.
- Webhook events with HMAC-SHA256 signatures and retries.
- Keys prefixed imc_live_, hashed at rest, revocable at any time.
02 / Capabilities
Built for automation, not just integrations
The API covers the objects an automation actually touches, and the webhooks tell you when to act.
API keys
On Professional and above, generate keys in Settings under Developer. Each key shows once, is stored as a hash, and can be revoked without touching the others. A key acts only on your own account, and client records it returns never include a social security number or a bank account number.
Webhooks
Subscribe an HTTPS endpoint to events across invoices, payments, clients, remittance advice and recurring invoices, or to all of them at once.
MCP server
Connect at https://mcp.invoicemyclients.com/mcp by signing in when your AI client supports it, or with an API key. Both need the Professional plan or above. The client gets tools for invoices, clients, payments, proposals, time, reports and collections; calls that would contact your clients are refused on live accounts, so sending stays in the app.
Signed and retried
Every delivery carries the event name, a timestamp and an HMAC-SHA256 signature in its headers. Failed deliveries retry after 5 and 25 seconds and are logged for inspection.
Rate limits
The MCP server is rate limited, 300 requests a minute by default. Key creation is limited to five keys per minute per account. List endpoints return 50 records by default and 100 at most.
Developer docs in the app
The Developer section in Settings shows your base URL, documents each endpoint and its parameters with curl examples, and has the MCP connection snippets for Cursor and Claude Code.
03 / Process
How to connect
Be on Professional or above, then create a key
API keys, the REST API and the MCP server are included on Professional, Business and Enterprise. Open Settings, then Developer, and generate an API key. Copy it now: only a masked version is shown afterwards. Interactive MCP clients can sign in instead of using a key.
Call the REST API
Send the key as a bearer token to list and create invoices and clients and to manage remittance advice, from your own code or an automation platform. New invoices are created as drafts; sending an invoice to a client is done in the app.
curl -H "Authorization: Bearer $IMC_API_KEY" \
"$IMC_API_BASE/v1/invoices?status=SENT&limit=10"Register a webhook
Under Settings, then Integrations, add your HTTPS endpoint and pick the events. Verify the HMAC signature on receipt and respond within 10 seconds.
Point an AI client at the MCP server
Add the server URL with Streamable HTTP. Clients that support MCP sign-in discover the login flow automatically; other clients send the API key as a bearer token.
export IMC_API_KEY="imc_live_your_api_key"
claude mcp add --transport http invoice-my-clients https://mcp.invoicemyclients.com/mcp \
--header "Authorization: Bearer $IMC_API_KEY"04 / FAQ
API FAQs
Which resources does the REST API cover?
Invoices (list, create as a draft, send as an e-invoice over Peppol or DBNA), clients (list, create) and remittance advice (list, create, read, update, mark as sent). There is no endpoint that emails an invoice to a client. Payments, proposals and time entries are available through the MCP server tools.
GET /v1/invoices
POST /v1/invoices
POST /v1/invoices/:id/send-einvoice
GET /v1/clients
POST /v1/clients
GET /v1/remittance-advice
POST /v1/remittance-advice
GET /v1/remittance-advice/:id
PATCH /v1/remittance-advice/:id
POST /v1/remittance-advice/:id/sendWhich webhook events can I subscribe to?
Events in five groups: invoice (created, updated, sent, viewed, voided, overdue and more), payment (initiated, succeeded, failed, recorded), client (created, updated), remittance advice (created, sent, acknowledged) and recurring invoices (scheduled, canceled). You can subscribe to all of them at once.
How are webhooks secured?
Each request is signed with HMAC-SHA256 over the timestamp, a dot and the body using your endpoint secret, sent in hexadecimal in the signature header alongside the event name and timestamp. Deliveries that fail are retried after 5 and 25 seconds and logged.
X-Webhook-Event: invoice.sent
X-Webhook-Timestamp: 2026-10-11T15:04:05.000Z
X-Webhook-Signature: <hex HMAC-SHA256 of "timestamp.body">Which plans include API access?
API keys, the REST API and the MCP server are included on the Professional plan and above: Professional, Business, Enterprise and White Label. Free and Starter have no API or MCP access of any kind, whether by API key or by signing in from an AI client, and there are no read-only keys. Webhooks are set up separately under Settings, then Integrations.
Is there a Zapier or Make integration?
The REST API was built with Zapier and Make in mind and works with their HTTP and webhook modules today (beta). There is no native app in either directory yet. Because they connect with an API key, they need the Professional plan or above.
Ship your first integration this afternoon
One key for the REST API and the MCP server, plus signed webhooks. Professional plan and above.
No credit card required to start.