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P402.io
Product / Orchestration

Agent tasks.
Streaming trace.

The A2A protocol lets agents communicate via JSON-RPC 2.0 task requests. Tasks stream live updates via SSE. Payment-required events are first-class — handled via the x402 extension, not as errors.

A2A referenceView live tasks
Task lifecycle

Five states

pendingTask received. Not yet assigned to a worker.
processingAgent is executing. SSE stream is open.
completedArtifacts available. Final state.
failedExecution error. Includes error message and requestId.
cancelledCancelled by caller before completion.
JSON-RPC 2.0

Methods

tasks/send

Submit a new task. Returns task object with initial state.

tasks/get

Retrieve task by ID. Includes artifacts if completed.

tasks/cancel

Cancel an in-progress task. Idempotent.

tasks/sendSubscribe

Submit and subscribe. Opens SSE stream for live updates.

All methods POST to POST /api/a2a with JSON-RPC 2.0 envelope.

Send a task
curl -X POST https://p402.io/api/a2a \
  -H "Authorization: Bearer $P402_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "tasks/send",
    "id": "1",
    "params": {
      "message": {
        "role": "user",
        "parts": [{
          "type": "text",
          "text": "Analyze this dataset"
        }]
      },
      "metadata": {
        "budget_usd": 0.50
      }
    }
  }'

# Response:
{
  "jsonrpc": "2.0",
  "id": "1",
  "result": {
    "id": "task_01HX...",
    "status": { "state": "pending" }
  }
}
Paid workflows

Payment-required tasks

When an agent requires payment, it emits a payment-required message — not an HTTP error. The orchestrator handles the x402 extension inline.

Agent sends
{ type: 'payment-required', data: X402PaymentRequired }
Client sends
{ type: 'payment-submitted', data: X402PaymentSubmitted }
Agent sends
{ type: 'payment-completed', data: X402PaymentCompleted }

Payment events appear as structured cards in the Tasks dashboard. Billing cap errors are returned as JSON-RPC -32000 block errors — the orchestrator does not crash.

SSE stream subscription
# Subscribe to task updates:
curl -N https://p402.io/api/a2a/stream?taskId=task_01HX... \
  -H "Authorization: Bearer $P402_API_KEY"

# Stream events:
data: {"type":"status","state":"processing"}
data: {"type":"payment-required","amount":"500000"}
data: {"type":"payment-completed","txHash":"0x..."}
data: {"type":"status","state":"completed"}
data: {"type":"artifact","text":"Analysis complete..."}
Decision trace

See every routing decision

The trace viewer streams every routing decision in real time — provider selected, cost saved, mandate checked, policy enforced, settlement attempted. Useful for debugging and auditing agentic workflows.

Open task dashboardA2A reference