Finance & ERP · Integration
Invoice Ninja
Add Invoice Ninja to your product for your customers, and give your AI agents governed access to it.
The hosted product answers on invoicing.co, while app.invoiceninja.com redirects, and self-hosted customers run their own domain, so the base URL belongs to the connection rather than the integration. Calls need X-API-TOKEN together with X-Requested-With set to XMLHttpRequest, because without it the application returns an HTML redirect and a JSON parser fails with no clue why. Each token is bound to a single company on a multi-company account, so switching company means a different token rather than a parameter. Related records are not embedded by default: an invoice comes back with a client_id and an invitations array only when you ask for them through the include parameter, and invitation records are what carry the public view links and the sent status. Deletes are three-state, since archive, delete and purge are distinct actions performed through the bulk action endpoint, and an archived invoice still exists and still affects balances. Amounts are stored against the company currency with the client currency held separately, so totals need the exchange rate on the record rather than a live rate. fastn holds each customer's host and token, keeps the company scope attached to that tenant, and handles rotation.
In your product
Embedded for your customers. Per-tenant auth, no per-customer code, maintained by fastn.
Let a customer connect their own Invoice Ninja company so invoices raised in your product appear in their books.
Create clients and invoices from your own order records, including line items and the correct client currency.
Read payments and outstanding balances so a customer sees who owes them money inside your app.
Push expenses and vendor bills captured in your product into their accounting view.
For your AI agents
Governed, audited access for the agents you build, through the MCP server.
Ask an agent which invoices are overdue and by how much, with every read audited per tenant.
Let an agent draft an invoice for review while sending stays a human approval step.
Have an agent reconcile payments against invoices and list the ones that do not match.
Example prompt
Which clients have invoices more than 30 days overdue, and what is the total outstanding?
Set up Invoice Ninja in 4 steps
- 01Enable the Invoice Ninja connector from your fastn dashboard.
- 02Have each customer authorise their own Invoice Ninja account, so calls run under their credentials rather than a shared key.
- 03Decide which invoices, payments and vendors your product needs, map those fields, then enable the actions and triggers you want.
- 04Call it from your product and expose it to your agents through the same governed connection.
Why teams use the Invoice Ninja integration
What you get by embedding it with fastn instead of building it yourself.
- Ship an Invoice Ninja integration without building it. Your customers connect their own Invoice Ninja account inside your product and work their invoices, payments and vendors there, with no per-customer code on your side.
- Handle the part that actually costs time: financial writes must be idempotent and reconcilable, because a duplicate is an accounting problem rather than a bug. fastn owns the auth, token refresh, rate limits, pagination and breaking-change fixes, so an Invoice Ninja update is not your on-call problem.
- One integration serves your product and your agents. The same governed Invoice Ninja connection powers in-product features and gives AI agents scoped, audited access, so you move financial records without hand-keying them between systems without wiring it twice.
Used by these teams
Compare with
NetSuite
QuickBooks
XeroOften used alongside
Tools the same teams tend to run next to Invoice Ninja, across other categories.
Shopify
Stripe
BigCommerce
AfterShipInvoice Ninja integration FAQ
How do I add an Invoice Ninja integration to my product?
Enable the Invoice Ninja connector in your fastn dashboard, then let each customer authenticate their own Invoice Ninja account. fastn handles the OAuth flow, token storage and refresh per tenant, so there is no Invoice Ninja client code in your app and no per-customer branch in your codebase. Setup is 4 steps.
Do my customers each connect their own Invoice Ninja account?
Yes. Every connection is scoped to the individual customer, so each authorises their own Invoice Ninja account and only ever sees their own invoices, payments and vendors. That per-tenant isolation is the point of an embedded integration: you support the long tail of customer setups without maintaining an integration per customer.
Can AI agents use this Invoice Ninja integration?
Yes. The same connection is exposed to your agents through the fastn MCP gateway, with permissions scoped per tenant and every call audited. Ask an agent which invoices are overdue and by how much, with every read audited per tenant.
Who maintains the Invoice Ninja integration?
fastn does. When Invoice Ninja changes an endpoint, deprecates a field or alters its auth, the fix lands in the connector rather than in your backlog, and your customers' connections keep working.
Is the Invoice Ninja integration safe for financial writes?
Writes are idempotent, so a retry after a timeout does not post a document twice, and every call is logged per tenant so an entry can be traced back to the event that created it. That matters more in finance than anywhere else, because a duplicate is a number somebody has to explain.
Can it handle each customer's own chart of accounts?
Yes. ERP deployments are configured to the business, so account structures, required fields and fiscal calendars differ per customer. Those are mapped per tenant as configuration, not hard-coded.
What about Invoice Ninja rate limits during a first import?
Backfills are throttled deliberately. ERP limits are often account-wide rather than per-integration, so an unthrottled import can exhaust a customer's allowance and disrupt their other integrations.
What can I build with the Invoice Ninja integration?
A common starting point: let a customer connect their own Invoice Ninja company so invoices raised in your product appear in their books. Teams also use it for the other use cases listed above, and expose it to agents for governed reads and writes.
How much does the Invoice Ninja integration cost?
It is included. Pricing is based on connected accounts, not on how many connectors you enable, so adding Invoice Ninja does not change your per-connector cost. You can start free with 3 connected accounts.
Add Invoice Ninja to your product
Start free with 3 connected accounts. No sales call required, and no per-customer integration code.