POST /billing/plan

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/billing/plan \
  -H "Authorization: Bearer $AGENTISEND_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{"tier":"free"}'

Node

import { AgentiSend } from 'agentisend';

const client = new AgentiSend(process.env.AGENTISEND_API_KEY);
const result = await client.request({
  method: 'POST',
  path: '/billing/plan',
  body: {
    "tier": "free"
  },
});

Python

import json, os, urllib.request

url = 'https://api.agentisend.com/billing/plan'
headers = {'Authorization': 'Bearer ' + os.environ['AGENTISEND_API_KEY']}
payload = json.dumps({"tier":"free"}).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: billing. Generated from openapi.json; the anchor post-billing-plan is the id the console's error fix links point at.

Parameters

• 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, appsumo_license_not_confirmed, appsumo_ticket_invalid, sign_in_check_required.
• 401 — No usable credential was sent. Codes: agent_signup_code_rejected, missing_api_key, session_required, mfa_required, appsumo_signature_invalid.
• 403 — The credential may not do this, or the account or key is stopped. Codes: sending_domain_blocked, young_domain_held, domain_sending_disabled, inbound_sender_refused, domain_not_verified, onboarding_recipient_not_a_member, onboarding_sender_unavailable, account_suspended, account_sandboxed, agent_unconfirmed, recipient_ramp, human_action_required, csrf_origin_rejected, charge_not_this_account, invalid_api_key, restricted_api_key, insufficient_role, invite_email_mismatch, domain_scope_violation, dedicated_ip_assigned_by_us, approval_required, staff_review_required, trust_paused, kill_switch_active.
• 404 — Nothing with this id exists on the account. Codes: billing_customer_missing, not_found, session_expired, support_ticket_not_found.
• 409 — The request conflicts with the current state. Codes: domain_already_exists, template_name_taken, template_alias_taken, template_in_use, segment_in_use, contact_resubscribe_required, email_still_scheduled, domain_verified_elsewhere, domain_not_claimable, return_path_subdomain_in_use, overage_not_on_plan, term_not_on_sale, subscription_active, portal_change_unavailable, already_in_account, idempotency_in_flight, idempotency_payload_mismatch, approval_expired, support_closed, support_reopen_expired, support_merge_conflict, support_reply_too_soon, appsumo_license_linked, appsumo_license_inactive, lifetime_sold_on_appsumo.
• 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, appsumo_lookup_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
{
  "appsumo": {
    "daily_send_cap": null,
    "emails_per_month": -9007199254740991,
    "license_key": "example",
    "max_domains": -9007199254740991,
    "max_seats": -9007199254740991,
    "name": "example",
    "retention_days": -9007199254740991,
    "tier": -9007199254740991
  },
  "appsumo_deal_url": "example",
  "appsumo_lifetime_notice": "example",
  "billing_configured": false,
  "billing_term": "month",
  "entitlements": {
    "included_emails_per_month": -9007199254740991,
    "max_domains": -9007199254740991,
    "max_seats": -9007199254740991,
    "overage_minor_per_1000_emails": -9007199254740991,
    "retention_days": -9007199254740991,
    "tier": "free"
  },
  "lifetime": {
    "emails_left": -9007199254740991,
    "emails_total": -9007199254740991,
    "emails_used": -9007199254740991,
    "max_emails_per_month": -9007199254740991,
    "name": "example",
    "refundable": false,
    "tier": "tier1"
  },
  "lifetime_on_sale": false,
  "lifetime_plans": [],
  "lifetime_refund_rule": "example",
  "lifetime_sales_channel": "own",
  "needs_plan_selection": false,
  "plan_source": "free",
  "plan_status": "none",
  "plans": [],
  "purchasable": [],
  "subscription": {
    "cancel_at_period_end": false,
    "current_period_end": "2026-09-04T09:14:00.000Z",
    "price_lookup_key": "example",
    "status": "example"
  },
  "terms_on_sale": [],
  "tier": "free",
  "viewer": {
    "can_purchase": false,
    "can_purchase_lifetime": false,
    "role": "owner"
  }
}

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.

• csrf_origin_rejected (403) — This request came from a page on another site, and it changes data. Fix: Call the API with an API key (Authorization: Bearer …) instead of a session cookie, or make the request from the console. Create a key in the console under Settings, API keys.
• 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.
• insufficient_role (403) — Your role on this account cannot make this change. Fix: Ask an owner to make the change, or to raise your role with PATCH /team/members/:id.
• 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.
• mfa_required (401) — This session has not completed two-factor authentication. Fix: Finish signing in at https://console.agentisend.com/verify with a code from your authenticator app, or one of your recovery codes. Manage the second factor in the console under Settings, Security.
• not_found (404, not_found) — Endpoint or resource does not exist. Fix: List that resource on this account and use an id from the list. For a domain, GET /domains accepts the id or the domain name. A path that is not a route is a typo in the URL.
• 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.
• session_required (401) — You are signed out. Fix: Sign in to the console, then retry. API keys cannot call this route.
• 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.