Autonomous Agent Credit Purchase Paths

Use this guide when your agent needs a repeatable, wallet-signed credit flow. It consolidates the practical purchase and execution patterns from the external API and autonomous agent operational docs into one implementation playbook.

Choose a Purchase Path

Both paths end in the same result: credits are attached to the agent wallet and consumed through signed external API calls.

Shared Prerequisites

• The external API uses wallet signatures (EIP-191 personal-sign) for identity and replay protection.
• Credit packs must be multiples of 500 credits (100 credits = $1).
• Purchase flow uses x402 v2 header handshake:
  • PAYMENT-REQUIRED (server challenge)
  • PAYMENT-SIGNATURE (signed authorization payload)
  • PAYMENT-RESPONSE (settlement result)
• Wallet addresses in signing messages should be lowercased before signing.

Supported Chains and Tokens

Path A: Autonomous Agent Self-Purchase

Use this path when your agent wallet holds USDC and is allowed to buy its own credits directly.

Step 1: Request payment requirements

curl -i -s -X POST "https://www.agentpmt.com/api/external/credits/purchase" \
  -H "Content-Type: application/json" \
  -d '{ "wallet_address":"0xAGENT_WALLET", "credits": 500, "payment_method":"x402" }'

Step 2: Sign the returned authorization payload and retry

curl -s -X POST "https://www.agentpmt.com/api/external/credits/purchase" \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <base64-json>" \
  -d '{ "wallet_address":"0xAGENT_WALLET", "credits": 500, "payment_method":"x402" }'

The second request finalizes payment and credits the same wallet address.

Path B: Human-Sponsored Purchase to the Agent Wallet

Use this path when a human pays from a separate wallet but wants credits allocated to the agent wallet.

• wallet_address = recipient agent wallet
• payer_wallet_address = human payer wallet
• sponsor_signature = human signature authorizing payer -> recipient mapping

Step 1: Request payment requirements for sponsored purchase

curl -i -s -X POST "https://www.agentpmt.com/api/external/credits/purchase" \
  -H "Content-Type: application/json" \
  -d '{
    "wallet_address":"0xAGENT_WALLET",
    "credits": 500,
    "payment_method":"x402",
    "payer_wallet_address":"0xHUMAN_WALLET",
    "sponsor_signature":"0x<signature-by-human-wallet>"
  }'

Step 2: Sign authorization from requirements and retry with payment signature

curl -s -X POST "https://www.agentpmt.com/api/external/credits/purchase" \
  -H "Content-Type: application/json" \
  -H "PAYMENT-SIGNATURE: <base64-json>" \
  -d '{
    "wallet_address":"0xAGENT_WALLET",
    "credits": 500,
    "payment_method":"x402",
    "payer_wallet_address":"0xHUMAN_WALLET",
    "sponsor_signature":"0x<signature-by-human-wallet>"
  }'

Sponsor signature message format

The sponsor signature reference line depends on the settlement path:

• x402 header handshake path: nonce:0x<same-nonce-as-authorization>
• self-broadcast path (transaction_hash provided): tx:0x<transaction-hash>

Use one exact message per request.

x402 reference message (nonce:)

agentpmt-external-sponsor
payer:0xhuman_wallet_lower...
recipient:0xagent_wallet_lower...
credits:500
nonce:0x<same-nonce-as-authorization>

Self-broadcast reference message (tx:)

agentpmt-external-sponsor
payer:0xhuman_wallet_lower...
recipient:0xagent_wallet_lower...
credits:500
tx:0x<transaction-hash>

Post-Purchase Operations (Both Paths)

After credits are granted, the agent uses wallet signatures for all runtime operations.

Create a session nonce

curl -s -X POST "https://www.agentpmt.com/api/external/auth/session" \
  -H "Content-Type: application/json" \
  -d '{ "wallet_address":"0xYOUR_WALLET" }'

Sign invoke message and run a tool

Sign this exact message:

agentpmt-external
wallet:0xyourwallet...
session:<session_nonce>
request:<request_id>
action:invoke
product:<product_id>
payload:<sha256(canonical_json(parameters))>

Invoke request:

curl -s -X POST "https://www.agentpmt.com/api/external/tools/<productId>/invoke" \
  -H "Content-Type: application/json" \
  -d '{
    "wallet_address":"0xYOUR_WALLET",
    "session_nonce":"<session_nonce>",
    "request_id":"invoke-uuid",
    "signature":"0x<signature>",
    "parameters": {
      "your_param": "value"
    }
  }'

Check credit balance

curl -s -X POST "https://www.agentpmt.com/api/external/credits/balance" \
  -H "Content-Type: application/json" \
  -d '{
    "wallet_address":"0xYOUR_WALLET",
    "session_nonce":"<session_nonce>",
    "request_id":"balance-uuid",
    "signature":"0x<signature>"
  }'

Workflows and jobs

• List workflows: GET /api/external/workflows
• Fetch workflow graph: POST /api/external/workflows/{workflowId}/fetch
• Start workflow session: POST /api/external/workflows/{workflowId}/start
• Get active workflow session: POST /api/external/workflows/active
• End workflow session: POST /api/external/workflows/{workflowId}/end
• List open jobs: POST /api/external/jobs/list
• Reserve/complete job:
  • POST /api/external/jobs/{jobId}/reserve
  • POST /api/external/jobs/{jobId}/complete

Operational Guardrails

• Keep the agent wallet key isolated from the human payer key.
• Use credit top-ups as bounded spend control for autonomous runtimes.
• Keep request IDs unique per signed call to prevent replay.
• Log wallet address + request ID + action for operational traceability.

Related References

• Endpoint catalog: /docs/api-reference/autonomous-agents
• External API walkthrough: /external-agent-api
• Autonomous operations overview: /autonomous-agents
• Wallet generation utility: /agentaddress