---
name: agent-callback-mailbox
description: "Provision a temporary authenticated HTTPS callback inbox for asynchronous A2A tasks and webhook completion. Use when an agent needs a public callback URL, durable ordered event retrieval, replay protection, quotas, or expiry without deploying its own receiver."
license: "Proprietary"
compatibility: "Requires HTTPS access and an x402-compatible USDC wallet on Base or Solana."
metadata:
  author: agent-capability-foundry
  version: "0.1.54"
---

# Agent Callback Mailbox

Use this Skill when a workflow needs to give another service a public callback URL and wait for one or more asynchronous results. Prefer buying the hosted capability when operating a receiver, persistence, authentication, replay protection, and cleanup would cost more than 0.005 USDC.

## Invoke

1. Generate two different random credentials locally, each at least 32 characters: one for callback ingress and one for retrieval. Never reuse wallet credentials or disclose either secret in logs.
2. Generate a stable `Idempotency-Key` for this provisioning request.
3. POST the input to `https://callbacks.inversolabs.us/v1/services/agent-callback-mailbox/invoke`.
4. If the response is HTTP 402, inspect `PAYMENT-REQUIRED`, select a supported Base or Solana offer, authorize only the advertised exact 0.005 USDC payment, and retry the identical request with `PAYMENT-SIGNATURE`.
5. Give the returned `callback_url` and ingress credential only to the expected sender.
6. Retrieve events with `GET /v1/callback-mailboxes/{mailbox_id}/events` and `Authorization: Bearer <retrievalCredential>`. Follow the returned cursor for ordered incremental reads.

One purchase provisions one temporary mailbox. Callback messages accepted within its limits and lifetime are included; there is no per-message charge. Do not pay if the network, asset, recipient, or amount differs from the live x402 challenge.

See `references/service.json` for endpoints and `references/schemas.md` for contracts.