Invoices you bill customers for, from draft to paid.

• Leave entityId out only when this key can reach exactly one business. When it can reach several, a call that omits it is refused; call GET /businesses for the ids.
• dateFrom and dateTo match the issue date and include both ends.
• To read the next page, pass the previous response's nextCursor. A null there means you already have everything.
• overdueOnly is applied to the page you asked for, not to the whole list, so a page can come back with fewer rows than limit, or none, while nextCursor is still set.
• An invoice's figures are in the invoice's own currency, which may not be US dollars, and the currency beside each figure says which. Every other amount on this surface is US dollars.

Needs the invoices:read permission. A Read only key has it.

curl "https://www.numm.io/api/v1/invoices?entityId=0190a1b2-c3d4-7e5f-8a9b-0c1d2e3f1002&status=sent" \
  -H "Authorization: Bearer nmo_live_REPLACE_WITH_YOUR_KEY"

{
  "invoices": [
    {
      "id": "0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007",
      "number": "ACME-0001",
      "status": "sent",
      "customer": "Acme Co",
      "issueDate": "2026-06-01",
      "dueDate": "2026-06-15",
      "total": {
        "cents": "10000",
        "formatted": "$100.00",
        "currency": "USD"
      },
      "paid": {
        "cents": "0",
        "formatted": "$0.00",
        "currency": "USD"
      },
      "balance": {
        "cents": "10000",
        "formatted": "$100.00",
        "currency": "USD"
      },
      "currency": "USD"
    }
  ],
  "nextCursor": null
}

• An invoice's figures are in the invoice's own currency, which may not be US dollars, and the currency beside each figure says which. Every other amount on this surface is US dollars.
• payUrl is the customer's own pay page and needs no sign-in. Anyone with the link can open the invoice and pay it, so treat it like the invoice email itself.

Needs the invoices:read permission. A Read only key has it.

curl "https://www.numm.io/api/v1/invoices/0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007" \
  -H "Authorization: Bearer nmo_live_REPLACE_WITH_YOUR_KEY"

{
  "id": "0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007",
  "number": "ACME-0001",
  "status": "sent",
  "customer": {
    "id": "0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1005",
    "name": "Acme Co"
  },
  "issueDate": "2026-06-01",
  "dueDate": "2026-06-15",
  "terms": "Net 15",
  "currency": "USD",
  "subtotal": {
    "cents": "10000",
    "formatted": "$100.00",
    "currency": "USD"
  },
  "tax": {
    "cents": "0",
    "formatted": "$0.00",
    "currency": "USD"
  },
  "total": {
    "cents": "10000",
    "formatted": "$100.00",
    "currency": "USD"
  },
  "paid": {
    "cents": "0",
    "formatted": "$0.00",
    "currency": "USD"
  },
  "balance": {
    "cents": "10000",
    "formatted": "$100.00",
    "currency": "USD"
  },
  "memo": null,
  "lines": [
    {
      "description": "Consulting",
      "quantity": "1",
      "unitPrice": {
        "cents": "10000",
        "formatted": "$100.00",
        "currency": "USD"
      },
      "amount": {
        "cents": "10000",
        "formatted": "$100.00",
        "currency": "USD"
      },
      "account": "Consulting Revenue"
    }
  ],
  "payments": [],
  "payUrl": "https://www.numm.io/pay/abc123"
}

• Leave entityId out only when this key can reach exactly one business. When it can reach several, a call that omits it is refused; call GET /businesses for the ids.
• unitPriceCents is whole cents, and quantity allows up to six decimal places. Each line's quantity must be greater than zero.
• issueDate defaults to the current date in UTC. dueDate defaults to issueDate plus the payment terms, taken from the customer, then the business, then your account. A dueDate before issueDate is refused.
• Every line amount, the subtotal, and the total must each stay under ten trillion dollars.
• currency is the invoice's own currency, and defaults to US dollars when you leave it out. It is not taken from the customer, even when the customer is set to another currency, which is how the app's own invoice form behaves too.
• unitPriceCents, and every figure the invoice reads back with, are cents of the invoice's own currency. Your books stay in US dollars: the conversion happens when the invoice is sent.
• Sending an invoice in another currency needs an exchange rate for its issue date. Until one has been fetched, POST /invoices/{id}/send is refused with validation_failed and the draft is left as it is.

Needs the invoices:write permission. Only a Read and write key has it.

curl -X POST "https://www.numm.io/api/v1/invoices" \
  -H "Authorization: Bearer nmo_live_REPLACE_WITH_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: 0190a1b2-c3d4-7e5f-8a9b-0c1d2e3fee00" \
  -d '{
  "entityId": "0190a1b2-c3d4-7e5f-8a9b-0c1d2e3f1002",
  "customerId": "0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1005",
  "lines": [
    {
      "description": "Consulting",
      "quantity": "1",
      "unitPriceCents": "10000",
      "accountId": "0190a1b2-c3d4-7e5f-8a9b-0c1d2e3f1003"
    }
  ]
}'

{
  "invoiceId": "0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007",
  "invoiceNumber": "ACME-0001",
  "webUrl": "https://www.numm.io/app/invoices/0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007"
}

This call takes an optional Idempotency-Key header. Repeat the same request with the same key within 24 hours and you get the first response back, with an idempotent-replayed: true header, and the work does not run twice. The same key with a different request is refused. See Idempotency and safe retries.

• Finalizing posts the invoice to the books and emails the customer before this call returns.
• There is no API call that undoes it.
• An invoice drafted in a currency other than US dollars needs an exchange rate for its issue date. Without one this call is refused with validation_failed, and the draft is left as it was. Try again once the day's rate has been fetched.

Needs the invoices:write permission. Only a Read and write key has it.

No request body.

curl -X POST "https://www.numm.io/api/v1/invoices/0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007/send" \
  -H "Authorization: Bearer nmo_live_REPLACE_WITH_YOUR_KEY" \
  -H "Idempotency-Key: 0190a1b2-c3d4-7e5f-8a9b-0c1d2e3fee00"

{
  "ok": true
}

This call takes an optional Idempotency-Key header. Repeat the same request with the same key within 24 hours and you get the first response back, with an idempotent-replayed: true header, and the work does not run twice. The same key with a different request is refused. See Idempotency and safe retries.

• The invoice has to be sent, viewed, or overdue, and the customer has to have an email address.
• A second reminder for the same invoice within 24 hours is refused with conflict.

Needs the invoices:write permission. Only a Read and write key has it.

No request body.

curl -X POST "https://www.numm.io/api/v1/invoices/0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007/remind" \
  -H "Authorization: Bearer nmo_live_REPLACE_WITH_YOUR_KEY" \
  -H "Idempotency-Key: 0190a1b2-c3d4-7e5f-8a9b-0c1d2e3fee00"

{
  "ok": true
}

This call takes an optional Idempotency-Key header. Repeat the same request with the same key within 24 hours and you get the first response back, with an idempotent-replayed: true header, and the work does not run twice. The same key with a different request is refused. See Idempotency and safe retries.

• amountCents must be greater than zero, and may not exceed the remaining balance.
• The invoice has to have been sent already, and must not be fully paid.
• method defaults to other, and paidAt defaults to the current date in UTC.
• method covers the payments you take yourself. Card payments arrive through Stripe and post on their own.
• The balance in the response leaves out any payment that was refunded.
• amountCents and the balance in the response are in the invoice's own currency, which may not be US dollars. Every other amount on this surface is US dollars.

Needs the invoices:write permission. Only a Read and write key has it.

curl -X POST "https://www.numm.io/api/v1/invoices/0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1007/payments" \
  -H "Authorization: Bearer nmo_live_REPLACE_WITH_YOUR_KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: 0190a1b2-c3d4-7e5f-8a9b-0c1d2e3fee00" \
  -d '{
  "amountCents": "4000",
  "method": "check"
}'

{
  "paymentId": "0190a1b2-c3d4-7e5f-9a9b-0c1d2e3f1009",
  "status": "partially_paid",
  "balance": {
    "cents": "6000",
    "formatted": "$60.00",
    "currency": "USD"
  }
}

This call takes an optional Idempotency-Key header. Repeat the same request with the same key within 24 hours and you get the first response back, with an idempotent-replayed: true header, and the work does not run twice. The same key with a different request is refused. See Idempotency and safe retries.