refund_invoice

THE RISK

Critical Risk

Why refund_invoice needs a policy

This tool directly moves money by refunding payments. Misuse allows an AI agent to initiate refunds on invoices without proper authorization, causing financial loss. This is a core financial operation with high blast radius and is the most severe risk category applicable.

From the tool's definition Tool name is 'refund_invoice' and description states it refunds a paid invoice (full or partial) via POST to /invoices/:id/refund. The server itself is explicitly for 'Agent-to-Agent Payment Protocol.'

Documented attack patterns abuse exactly the kind of access refund_invoice gives an agent:

POLICY

How to control refund_invoice

PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Ap2, and nothing reaches the server without passing your rules. This is the rule we recommend for refund_invoice:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "refund_invoice": {
      "deny_if": [
        {
          "conditions": [],
          "on_deny": "Requires human approval."
        }
      ]
    }
  }
}

Any call to refund_invoice is blocked until a human approves it. The rest of the server keeps working.

Create a free account and register Mcp Ap2 — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

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EXPLORE

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Go deeper

Critical-risk tools in Mcp Ap2 → Every critical-risk tool this server exposes, in one view.
All critical-risk MCP tools → Every critical-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Human-in-the-loop → When a tool call should wait for a person — and when policy can decide alone.
Tool call approval → Approval gates on individual tool calls: auto-allow, prompt, or deny.
How to Add Spending Controls to Any MCP Agent →
Rate Limiting MCP Tool Calls: A Practical Guide →

FAQ

Questions about refund_invoice

What does the refund_invoice tool do? +

Refund a paid invoice (full or partial). Endpoint: POST /invoices/:id/refund. It is categorised as a Financial tool in the Mcp Ap2 MCP Server, which means it involves financial transactions. Block by default and require explicit approval.

How do I enforce a policy on refund_invoice? +

Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for refund_invoice: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Mcp Ap2. Nothing to install.

What risk level is refund_invoice? +

refund_invoice is a Financial tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.

Can I rate-limit refund_invoice? +

Yes. Add a rate_limit block to the refund_invoice rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block refund_invoice completely? +

Set action: deny in the PolicyLayer policy for refund_invoice. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides refund_invoice? +

refund_invoice is provided by the Mcp Ap2 MCP server (@codespar/mcp-ap2). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Mcp Ap2 tool call.

Start from Mcp Ap2, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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