cURL

curl https://invoice.horizonpay.co/api/v1/invoices/in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8/send \
  -H "Authorization: Bearer $INVOICE_AI_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{ "to": "[email protected]" }'

import InvoiceAI from '@horizonpay/invoice-ai'

const invoiceai = new InvoiceAI() // reads INVOICE_AI_API_KEY

// Retries reuse one Idempotency-Key; pass { idempotencyKey } to set your own.
const sent = await invoiceai.invoices.send('in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8', {
  to: '[email protected]',
})
console.log(sent.data.number, sent.emailed_to)

from invoice_ai import InvoiceAI

client = InvoiceAI()  # reads INVOICE_AI_API_KEY

# Retries reuse one Idempotency-Key; pass idempotency_key=... to set your own.
sent = client.invoices.send(
    "in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8",
    to="[email protected]",
)
print(sent.data.number, sent.emailed_to)

{
  "data": {
    "id": "in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8",
    "object": "invoice",
    "number": "INV-0042",
    "status": "open",
    "customer": "cus_Nf3kQ8pR2mX7vB1cT9wL4sZ6",
    "currency": "USD",
    "collection_method": "send_invoice",
    "issue_date": "2026-09-22",
    "due_date": "2026-10-22",
    "description": "Consulting retainer.",
    "footer": null,
    "subtotal": 2550000,
    "discount": 0,
    "taxable": 2550000,
    "tax": 0,
    "total": 2550000,
    "amount_due": 2550000,
    "amount_in_words": "Twenty Five Thousand Five Hundred USD Only",
    "public_url_token": "2b7e4c1a-9f3d-4e68-8a5b-0d1c7f3e9a46",
    "finalized_at": "2026-09-22T10:00:00.000Z",
    "paid_at": null,
    "voided_at": null,
    "void_reason": null,
    "created": "2026-09-22T09:30:00.000Z",
    "updated": "2026-09-22T10:00:00.000Z",
    "lines": {
      "data": [
        {
          "id": "ii_Da4Vq9Ns2Kx7Bm3Yt8Rc1Lp6",
          "object": "invoiceitem",
          "price": "price_Jc5Tn8Wq1Ze6Ra3Ym9Ub2Gs7",
          "product": "prod_Hy7Rq2Lm9Xc4Vb8Nt3Kd6Pw1",
          "description": "Consulting retainer",
          "quantity": 1,
          "unit": "NOS",
          "unit_amount": 2500000,
          "amount": 2500000,
          "discount_percent": 0,
          "tax_rate": 0,
          "tax_amount": 0
        },
        {
          "id": "ii_Ew8Hz3Jc6Tq1Ms5Nv9Kb2Xr4",
          "object": "invoiceitem",
          "price": null,
          "product": null,
          "description": "Onboarding workshop",
          "quantity": 1,
          "unit": "NOS",
          "unit_amount": 50000,
          "amount": 50000,
          "discount_percent": 0,
          "tax_rate": 0,
          "tax_amount": 0
        }
      ]
    }
  },
  "emailed_to": "[email protected]"
}

Invoices

Send an invoice

Emails the invoice PDF and a link to its public page to to, or else the customer email on the invoice. A draft is finalized first (no invoices:finalize scope needed). Open and paid invoices can be re-sent; void ones cannot.

Requires a verified account email — until then this returns 409 invalid_state.

Rate limits: 10 sends per hour per API key, and 50 per hour per account across every key and the dashboard (429 rate_limited, with Retry-After).

If the email fails after finalizing, the response is 502 upstream_failed and the number stays spent; retry the send. Emits invoice.emailed (or invoice.email_failed), plus invoice.finalized when it finalized.

Scope: invoices:send

Idempotency: Idempotency-Key required (428 without it). A retry with the same key and body replays the first response (Idempotent-Replayed: true); the same key with a different body is a 422 idempotency_mismatch.

POST

invoices

{id}

send

cURL

curl https://invoice.horizonpay.co/api/v1/invoices/in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8/send \
  -H "Authorization: Bearer $INVOICE_AI_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{ "to": "[email protected]" }'

import InvoiceAI from '@horizonpay/invoice-ai'

const invoiceai = new InvoiceAI() // reads INVOICE_AI_API_KEY

// Retries reuse one Idempotency-Key; pass { idempotencyKey } to set your own.
const sent = await invoiceai.invoices.send('in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8', {
  to: '[email protected]',
})
console.log(sent.data.number, sent.emailed_to)

from invoice_ai import InvoiceAI

client = InvoiceAI()  # reads INVOICE_AI_API_KEY

# Retries reuse one Idempotency-Key; pass idempotency_key=... to set your own.
sent = client.invoices.send(
    "in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8",
    to="[email protected]",
)
print(sent.data.number, sent.emailed_to)

{
  "data": {
    "id": "in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8",
    "object": "invoice",
    "number": "INV-0042",
    "status": "open",
    "customer": "cus_Nf3kQ8pR2mX7vB1cT9wL4sZ6",
    "currency": "USD",
    "collection_method": "send_invoice",
    "issue_date": "2026-09-22",
    "due_date": "2026-10-22",
    "description": "Consulting retainer.",
    "footer": null,
    "subtotal": 2550000,
    "discount": 0,
    "taxable": 2550000,
    "tax": 0,
    "total": 2550000,
    "amount_due": 2550000,
    "amount_in_words": "Twenty Five Thousand Five Hundred USD Only",
    "public_url_token": "2b7e4c1a-9f3d-4e68-8a5b-0d1c7f3e9a46",
    "finalized_at": "2026-09-22T10:00:00.000Z",
    "paid_at": null,
    "voided_at": null,
    "void_reason": null,
    "created": "2026-09-22T09:30:00.000Z",
    "updated": "2026-09-22T10:00:00.000Z",
    "lines": {
      "data": [
        {
          "id": "ii_Da4Vq9Ns2Kx7Bm3Yt8Rc1Lp6",
          "object": "invoiceitem",
          "price": "price_Jc5Tn8Wq1Ze6Ra3Ym9Ub2Gs7",
          "product": "prod_Hy7Rq2Lm9Xc4Vb8Nt3Kd6Pw1",
          "description": "Consulting retainer",
          "quantity": 1,
          "unit": "NOS",
          "unit_amount": 2500000,
          "amount": 2500000,
          "discount_percent": 0,
          "tax_rate": 0,
          "tax_amount": 0
        },
        {
          "id": "ii_Ew8Hz3Jc6Tq1Ms5Nv9Kb2Xr4",
          "object": "invoiceitem",
          "price": null,
          "product": null,
          "description": "Onboarding workshop",
          "quantity": 1,
          "unit": "NOS",
          "unit_amount": 50000,
          "amount": 50000,
          "discount_percent": 0,
          "tax_rate": 0,
          "tax_amount": 0
        }
      ]
    }
  },
  "emailed_to": "[email protected]"
}

Authorizations

Authorization

string

header

required

An Invoice-AI API key sent as Authorization: Bearer inv_live_….

Create keys in Settings → API keys; the secret is shown once. Each key carries scopes, and every operation lists the scope it needs (x-required-scope):

business:read — Read your business profile, tax ID and bank details
clients:read — List and read your clients
clients:write — Create, update and archive clients
products:read — List and read products and prices
products:write — Create, update and archive products and prices
invoices:read — List and read invoices, including PDFs
invoices:write — Create, edit and delete drafts
invoices:finalize — Finalize invoices and void them
invoices:send — Email invoices to your clients
payments:write — Mark invoices as paid
webhooks:manage — Manage webhook endpoints

Keys cannot be created or revoked through the API, so a leaked key cannot mint more keys.

Headers

Idempotency-Key

string

required

A unique key per distinct operation (a UUID works), reused only when retrying that same request. Up to 255 characters; stored for 24 hours.

Maximum string length: 255

Example:

"6f1c2d9e-8a4b-4c3f-9e7d-2b5a1c8f4e30"

Path Parameters

string

required

The invoice, in_… or UUID.

Example:

"in_Pb2Xk7Mv4Qs9Lr1Wd6Tn3Fh8"

Body

application/json

string

Recipient email. Defaults to the customer email recorded on the invoice; one of the two is required.

Example:

"[email protected]"

Response

Sent. The invoice (finalized if it was a draft, with lines) plus the address it went to.

data

object

required

The invoice, finalized if it was a draft, with lines.

Show child attributes

emailed_to

string

required

The address the email was sent to: to, or the customer email.

Example:

"[email protected]"

Overview

Endpoints

Send an invoice

Authorizations

Headers

Path Parameters

Body

Response