# MCP Transaction Gateway

> MCP Transaction Gateway is a paid API for AI agents from phion.systems, paid per call via x402, $0.004/call, status unknown (last checked 2026-10-23).

Binds an MCP tool-call identity to a payment transaction without silently granting spending authority

## Facts

- Endpoint: POST https://phion.systems/v1/paid/trust/mcp-transaction-gateway?utm_source=zero.xyz
- Price: $0.004/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-23
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/mcp-transaction-gateway-6d3667b6
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_3mdvUl_5yG7CcrVZGtD6E

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 mcp-transaction-gateway-6d3667b6 -d '<json body>'
```

Example prompt: Before allowing this MCP tool call to proceed with payment, bind the tool-call identity to the transaction so spending authority isn't silently granted — I need an explicit authorization receipt tying this specific invocation to the transaction.

## When to prefer this

Use this endpoint when an MCP-based agent needs to initiate or participate in a payment transaction and you require explicit, auditable identity binding to that transaction — specifically to prevent the agent from silently inheriting spending authority. Prefer this over generic payment authorization when the caller is an MCP tool and least-privilege enforcement plus provenance attestation are required.

## Known failure modes

- Missing or malformed MCP tool-call identity results in a 400 error and rejection
- Transaction reference not found or already bound returns a conflict error
- Attempt to bind with mismatched identity/transaction scope is rejected to prevent authority escalation
- Malformed request body (empty schema) may cause validation errors if required fields are absent
- Network or upstream service errors return 5xx with no binding issued

## How this service works

Bind MCP tool-call identity to a transaction without silently granting authority

## Output

A signed receipt or attestation confirming that the specified MCP tool-call identity has been explicitly bound to the transaction, with no implicit or ongoing spending authority granted beyond the declared scope.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input",
  "output"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "body"
   ],
   "properties": {
    "body": {
     "type": "object",
     "additionalProperties": true
    }
   }
  },
  "output": {
   "type": "object",
   "required": [
    "example"
   ],
   "properties": {
    "example": {
     "type": "object",
     "additionalProperties": true
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json"
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/mcp-transaction-gateway-6d3667b6/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from phion.systems](https://www.zero.xyz/host/phion.systems/llms.txt)