Get last authorized invoice number for a point of sale and type
AI agents call get_last_invoice_number to retrieve information from Mcp Ap2 without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool queries and retrieves the last authorized invoice number, which is a read-only operation. It does not create, modify, delete, or execute any actions—it simply fetches existing data. Although the tool operates within a financial payment protocol context (AP2), it performs no financial transactions, money movement, or commitments.
From the tool's definition Tool name 'get_last_invoice_number' and description 'Get last authorized invoice number for a point of sale and type' indicate a retrieval operation with no modification or side effects.
Documented attack patterns abuse exactly the kind of access get_last_invoice_number gives an agent:
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 get_last_invoice_number:
{
"version": "1",
"default": "deny",
"tools": {
"get_last_invoice_number": {}
}
}get_last_invoice_number is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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Get last authorized invoice number for a point of sale and type. It is categorised as a Read tool in the Mcp Ap2 MCP Server, which means it retrieves data without modifying state.
Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for get_last_invoice_number: 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.
get_last_invoice_number is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the get_last_invoice_number 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.
Set action: deny in the PolicyLayer policy for get_last_invoice_number. 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.
get_last_invoice_number 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.
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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