POST /audiences/{audienceId}/contacts

Request

The same call in curl, Node and Python. A path id in the sample is a placeholder.

curl

curl -sS -X POST https://api.agentisend.com/audiences/9c8f8f0e-3d1a-4d3f-9a1e-2b7c1a0f5e42/contacts \
  -H "Authorization: Bearer $AGENTISEND_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"email":"customer@example.com"}'

Node

import { AgentiSend } from 'agentisend';

const client = new AgentiSend(process.env.AGENTISEND_API_KEY);
const result = await client.request({
  method: 'POST',
  path: '/audiences/9c8f8f0e-3d1a-4d3f-9a1e-2b7c1a0f5e42/contacts',
  body: {
    "email": "customer@example.com"
  },
});

Python

import json, os, urllib.request

url = 'https://api.agentisend.com/audiences/9c8f8f0e-3d1a-4d3f-9a1e-2b7c1a0f5e42/contacts'
headers = {'Authorization': 'Bearer ' + os.environ['AGENTISEND_API_KEY']}
payload = json.dumps({"email":"customer@example.com"}).encode()
headers['Content-Type'] = 'application/json'
request = urllib.request.Request(url, data=payload, headers=headers, method='POST')
print(urllib.request.urlopen(request).read().decode())

Tag: contacts. Generated from openapi.json; the anchor post-audiences-audienceid-contacts is the id the console's error fix links point at.

Parameters

• audienceId path · string · required
• Idempotency-Key header · string · optional — Makes this call safe to retry. Send the same key with the same body and the original response is replayed instead of the work happening twice. Keys are 1-256 characters and are remembered for 7 days. While the first attempt is still running, a second call with that key returns 409 idempotency_in_flight (Resend calls this concurrent_idempotent_requests); the same key with a different body returns 409 idempotency_payload_mismatch (Resend: invalid_idempotent_request). Resend-Idempotency-Key is accepted as the same header.
• Resend-Idempotency-Key header · string · optional — Alias of Idempotency-Key. Idempotency-Key wins if both are sent.

Request body

Responses

• 201 — Success
• 400 — The request is malformed or a field failed validation. Codes: validation_error, invalid_idempotency_key, invalid_cursor, plan_not_purchasable, stripe_signature_invalid, support_upload_rejected, sign_in_check_required.
• 409 — The request conflicts with the current state. Codes: domain_already_exists, template_name_taken, template_in_use, segment_in_use, contact_resubscribe_required, domain_verified_elsewhere, return_path_subdomain_in_use, overage_not_on_plan, term_not_on_sale, subscription_active, already_in_account, idempotency_in_flight, idempotency_payload_mismatch, approval_expired, support_closed, support_reopen_expired, support_merge_conflict.
• 413 — The request body is larger than this operation accepts. Codes: payload_too_large, support_upload_too_large.
• 415 — The request body is not JSON. Codes: unsupported_media_type.
• 429 — A rate, quota or ramp ceiling was reached. Codes: onboarding_daily_cap_reached, trust_throttled, invite_limit_reached, rate_ceiling_exceeded, daily_quota_exceeded, monthly_quota_exceeded, rate_limit_exceeded, support_rate_limited.
• 500 — Something failed on our side. Codes: internal_server_error.

Response headers

• ratelimit-limit — Messages this API key may spend in one 60-second window.
• ratelimit-remaining — Messages left in the current window.
• ratelimit-reset — Seconds until the current window resets and the budget refills.

Response example

201
{
  "created_at": "2026-09-04T09:14:00.000Z",
  "email": "example",
  "first_name": "example",
  "id": "9c8f8f0e-3d1a-4d3f-9a1e-2b7c1a0f5e42",
  "last_name": "example",
  "object": "contact",
  "properties": {},
  "property_types": {},
  "status": "example",
  "unsubscribed": false,
  "updated_at": "2026-09-04T09:14:00.000Z"
}

Errors

The codes this operation can answer with, and what to do about each. Every one arrives with its code, message, fix and docs_url.

• contact_resubscribe_required (409) — This address asked not to be contacted, so marking the contact active leaves that in place. Fix: POST /contacts/:id/resubscribe with consent_source and consent_at after the person opts back in. The id can be the contact id or the email address. A spam report is not lifted by that call.
• idempotency_in_flight (409) — A request with this Idempotency-Key is still in progress. Fix: Wait and retry with the same Idempotency-Key to receive the original response.
• idempotency_payload_mismatch (409) — Same Idempotency-Key was used with a different payload. Fix: Reuse the exact same body for retries, or send a new Idempotency-Key for a new request.
• internal_server_error (500, internal_server_error) — Unexpected error. Fix: Retry ONCE after a short pause, with the same Idempotency-Key so the retry cannot double-send. If it fails again, stop retrying and report the x-request-id from the response — that id is what identifies this exact failure in support.
• invalid_idempotency_key (400) — Idempotency-Key must be 1-256 characters. Fix: Send a non-empty Idempotency-Key header of at most 256 characters.
• payload_too_large (413) — Request body is larger than this endpoint accepts. Fix: Send a smaller body. Most endpoints accept 1 MB. Sends (POST /emails, /emails/batch, replies) and template, broadcast and automation edits accept 50 MB, which fits 40 MB of attachments after base64. /mcp accepts 1 MB per JSON-RPC call.
• rate_limit_exceeded (429, rate_ceiling_exceeded, rate_limit_exceeded) — Too many requests. Fix: Back off and retry honoring the Retry-After header.
• unsupported_media_type (415) — This endpoint does not accept that content type. Fix: Send the body as JSON with `Content-Type: application/json`.
• validation_error (400, domain_not_verified, invalid_parameter, validation_error) — Error in one or more fields. Fix: Correct the fields listed in the error details and retry the request.