castomAPI
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POST /v1/zapier/hooks/subscribe 1 token API key Zapier

Register a Zapier or third-party REST Hook subscription for real-time…

Register a Zapier or third-party REST Hook subscription for real-time event notifications Delivery is at-least-once. housekeeping requeues stalled deliveries, so a subscriber may receive a duplicate and should deduplicate on the X-CastomAPI-Delivery-Id header.

POST

Request

  • x-api-key: <your-api-key>
  • Content-Type: application/json

Response 

{
  "createdAt": "2026-09-08T10:00:00Z",
  "event": "<event>",
  "message": "Hello from castomAPI.",
  "secret": "<secret>",
  "status": "success",
  "subscriptionId": "sub_112060",
  "targetUrl": "https://example.com/page",
  "tokensDeducted": 1
}
The response below is a mock built from the endpoint's own schema — no request leaves this page. Edit the body, press Send, read the shape you will get back. Run it for real in the dashboard →

What it does

Register a Zapier or third-party REST Hook subscription for real-time event notifications Delivery is at-least-once. housekeeping requeues stalled deliveries, so a subscriber may receive a duplicate and should deduplicate on the X-CastomAPI-Delivery-Id header.

Request

Body

FieldTypeRequiredDescription
eventenumyesEvent topic trigger to subscribe to One of: balance.low, endpoint.error, job.completed, security.alert, usage.threshold, discord.interaction_received, twitch.stream.online, twitch.stream.offline….
metadataobjectnoOptional user context metadata to attach to the subscription
secretstringnoOptional custom HMAC signing secret to verify payload signatures
targetUrlstringyesURL where castomAPI will dispatch POST event webhooks

Example request

{
  "event": "balance.low",
  "metadata": {},
  "secret": "<secret>",
  "targetUrl": "https://example.com/page"
}

Response

FieldTypeDescription
createdAtstring
eventstring
messagestring
secretstringThe HMAC signing secret for this subscription. Returned once at creation; store it to verify the X-CastomAPI-Signature header -- it cannot be retrieved later.
statusstring
subscriptionIdstring
targetUrlstring
tokensDeductedinteger

Example response

{
  "createdAt": "2026-09-08T10:00:00Z",
  "event": "<event>",
  "message": "Hello from castomAPI.",
  "secret": "<secret>",
  "status": "success",
  "subscriptionId": "sub_112060",
  "targetUrl": "https://example.com/page",
  "tokensDeducted": 1
}

Errors

Every error answers with the same envelope: an HTTP status, a machine code and a sentence.

400The body or a parameter failed validation. The details array names the field.
401No key, a revoked key or a wrong header. Send x-api-key.
402The wallet cannot cover this call. Top up or wait for the monthly grant.
404The resource does not exist, or it is not yours. Both answer identically and cost nothing.
429Over the per-minute quota of your tier. Back off and retry.
5xxUpstream refused or timed out. The call is not billed.

Code

curl -X POST 'https://app.castomapi.com/v1/zapier/hooks/subscribe' \
  -H 'x-api-key: <your-api-key>' \
  -H 'Content-Type: application/json' \
  -d '{"event": "balance.low", "metadata": {}, "secret": "<secret>", "targetUrl": "https://example.com/page"}'
const res = await fetch('https://app.castomapi.com/v1/zapier/hooks/subscribe', {
  method: 'POST',
  headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
  body: JSON.stringify({"event": "balance.low", "metadata": {}, "secret": "<secret>", "targetUrl": "https://example.com/page"})
});
const data = await res.json();
console.log(data);
import { request } from 'node:https';

// Node 18+ has fetch built in
const res = await fetch('https://app.castomapi.com/v1/zapier/hooks/subscribe', {
  method: 'POST',
  headers: { 'x-api-key': '<your-api-key>', 'Content-Type': 'application/json' },
  body: JSON.stringify({"event": "balance.low", "metadata": {}, "secret": "<secret>", "targetUrl": "https://example.com/page"})
});
const data = await res.json();
console.log(data);
import requests

res = requests.post(
    'https://app.castomapi.com/v1/zapier/hooks/subscribe',
    headers={'x-api-key': '<your-api-key>'},
    json={"event": "balance.low", "metadata": {}, "secret": "<secret>", "targetUrl": "https://example.com/page"},
    timeout=30,
)
print(res.json())
<?php
$ch = curl_init('https://app.castomapi.com/v1/zapier/hooks/subscribe');
curl_setopt_array($ch, [
    CURLOPT_CUSTOMREQUEST => 'POST',
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => ['x-api-key: <your-api-key>', 'Content-Type: application/json'],
    CURLOPT_POSTFIELDS => json_encode(['event' => 'balance.low', 'metadata' => [], 'secret' => '<secret>', 'targetUrl' => 'https://example.com/page']),
]);
$data = json_decode(curl_exec($ch), true);
print_r($data);

Cost and limits

This operation costs 1 token. A call that fails is never billed. Every account gets 1000 free tokens a month; paid balances never expire.

Rate limits per minute

No key10
Free60
Pro300
Enterprise1200

Docs → Pricing

Questions

What does Register a Zapier or third-party REST Hook subscription for real-time… cost?

1 token per successful call, debited from your wallet after the response. Failed calls are free. Every account receives 1000 free tokens a month.

How do I authenticate?

Send your key in the x-api-key header. One key covers every metered endpoint; there is nothing to enable per endpoint.

Can I send an Authorization: Bearer token instead?

Not for a metered endpoint — those take the x-api-key header and nothing else. Bearer tokens belong to the account side: the dashboard and account APIs accept a JWT session, and castomapi-auth issues those through a standard OAuth2 handshake, with authorization code, client credentials and refresh grants. The auth service page covers it.

What are the limits?

10 requests a minute per IP with no key at all, 60 a minute on the free tier, 300 on Pro, 1200 on Enterprise. Above the no-key tier the quota is per account, across every endpoint.

OpenAPI: https://app.castomapi.com/docs/json