# RelayBox 24-Hour Callback Inbox

> RelayBox 24-Hour Callback Inbox is a paid API for AI agents from relaybox-phcqcexu4a-uc.a.run.app, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-27).

Provisions a durable, ordered 24-hour callback inbox with acknowledgment and replay support for reliable event delivery to AI agents or webhooks.

## Facts

- Endpoint: POST https://relaybox-phcqcexu4a-uc.a.run.app/v1/inboxes?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-27
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/relaybox-24-hour-callback-inbox-31306c11
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_cI-QpLoit4bwUf0EgcL_O

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability relaybox-24-hour-callback-inbox-31306c11 -d '<json body>'
```

Example prompt: Set up a 24-hour durable callback inbox for me — I need one with ordered event delivery and replay support so my agent can reliably catch async responses even if it goes offline briefly.

## When to prefer this

Choose RelayBox when you need a durable, short-lived callback inbox with guaranteed ordered event delivery, acknowledgment, and replay capability — especially for AI agent workflows where the consumer may be intermittently offline and cannot afford to miss async callbacks. Prefer this over generic webhook receivers (e.g. webhook.site, requestbin) when ordered delivery and replay are critical requirements and a 24-hour window is sufficient.

## Known failure modes

- Payment failure: USDC payment of $0.01 not confirmed, inbox not created
- Invalid plan: only 'inbox-24h' is accepted as a plan value — other values rejected
- Inbox expiry: inbox automatically expires after 24 hours, events no longer deliverable
- Missing recovery headers: events cannot be replayed without the correct headers returned at creation
- Service unavailability: Google Cloud Run cold-start or quota limits may cause transient 503 errors

## How this service works

Buy a 24-hour durable callback inbox. Ordered events, acknowledgment and replay. See /llms.txt for required recovery headers.

## Output

Returns a provisioned inbox resource including a unique callback URL, inbox ID, expiry time (24 hours from creation), and the required recovery/replay headers (as documented in /llms.txt) needed to retrieve ordered events and acknowledge receipt.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "plan": {
   "const": "inbox-24h"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/relaybox-24-hour-callback-inbox-31306c11/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from relaybox-phcqcexu4a-uc.a.run.app](https://www.zero.xyz/host/relaybox-phcqcexu4a-uc.a.run.app/llms.txt)