# Agent Identity Registration via x402

> Agent Identity Registration via x402 is a paid API for AI agents from agent-id-x402-production.up.railway.app, paid per call via x402, $0.1/call, status unknown (last checked 2026-09-15).

Issues a signed, non-transferable agent identity credential binding an Ed25519 public key to a paying wallet address as anti-Sybil proof of distinct, paying agent registration.

## Facts

- Endpoint: POST https://agent-id-x402-production.up.railway.app/register
- Price: $0.1/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/agent-identity-registration-via-x402-f72c90e5
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_uMp5qM0oNdGYRoK0t5Evu

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 agent-identity-registration-via-x402-f72c90e5 -d '<json body>'
```

Example prompt: Register my agent's identity using my Ed25519 public key 'a1b2c3...64hexchars' and a delegation signature over my wallet address '0xabcd...1234' so I get a signed, non-transferable identity credential proving I'm a distinct, previously registered, paying agent.

## When to prefer this

Choose this endpoint when an AI agent needs to establish a cryptographically verifiable, non-transferable identity credential that proves it is a distinct, paying, previously registered entity — particularly in anti-Sybil, multi-agent, or gated-access contexts where duplicate or fake agents must be excluded. Prefer this over generic OAuth or API-key auth when on-chain wallet binding and Ed25519-based agent authentication are required.

## Known failure modes

- 402 Payment Required — request was not accompanied by valid x402 payment; response includes full registration instructions
- Invalid auth_pubkey — Ed25519 public key is not exactly 64 hex characters
- Invalid delegation_signature — signature does not verify against the auth private key over the expected ASCII message and wallet address
- Missing required fields — auth_pubkey not provided in body
- Conflicting binding parameters — both delegation_signature and salt provided or neither provided
- Wallet address already registered — attempting to re-register a previously used wallet
- Key already bound — Ed25519 key already associated with another identity

## How this service works

Pay once, get a unique non-transferable agent identity tag: an issuer-signed credential binding your Ed25519 auth key to your paying wallet. Anti-Sybil proof of being a distinct, previously registered, paying agent. Unpaid 402 returns full instructions.

## Output

An issuer-signed credential (identity tag) that cryptographically binds the submitted Ed25519 public key to the paying wallet address, serving as non-transferable anti-Sybil proof that this is a distinct, previously registered, paying agent. An unpaid request returns a 402 response with full registration instructions.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "salt": {
   "type": "string",
   "description": "Hex salt — only for the nonce-commitment binding method."
  },
  "auth_pubkey": {
   "type": "string",
   "description": "Raw Ed25519 public key, hex (64 chars). Generate locally; the private key never leaves your machine."
  },
  "delegation_signature": {
   "type": "string",
   "description": "Ed25519 signature, hex (128 chars), by the auth private key over the ASCII message 'agent-id-x402/delegation/v1:' + your paying wallet address lowercased. Alternative: send 'salt' instead and set the payment's EIP-3009 nonce to keccak256(auth_pubkey||salt)."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/agent-identity-registration-via-x402-f72c90e5/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agent-id-x402-production.up.railway.app](https://www.zero.xyz/host/agent-id-x402-production.up.railway.app/llms.txt)