Apply credit to an invoice
AI agents use whmcs_apply_credit to create or update resources in Whmcs — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Whmcs environment.
This tool modifies invoice state by applying credit, which is a write operation that changes data in the WHMCS billing system. While it involves financial records, the action itself (applying credit) is reversible—credits can be removed or adjusted. It does not move actual money, commit financial obligations, or execute code; therefore it is categorized as Write rather than Financial or Execute.
From the tool's definition Tool name 'whmcs_apply_credit' and description 'Apply credit to an invoice' indicate a reversible modification of financial records.
Documented attack patterns abuse exactly the kind of access whmcs_apply_credit gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Whmcs, and nothing reaches the server without passing your rules. This is the rule we recommend for whmcs_apply_credit:
{
"version": "1",
"default": "deny",
"tools": {
"whmcs_apply_credit": {
"limits": [
{
"counter": "whmcs_apply_credit_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}whmcs_apply_credit stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
Free to start. No card required.
Apply credit to an invoice. It is categorised as a Write tool in the Whmcs MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Whmcs MCP server in PolicyLayer and add a rule for whmcs_apply_credit: 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 Whmcs. Nothing to install.
whmcs_apply_credit is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the whmcs_apply_credit 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 whmcs_apply_credit. 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.
whmcs_apply_credit is provided by the Whmcs MCP server (scarecr0w12/whmcs-mcp-tool). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Whmcs, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
62 Whmcs tools catalogued and risk-classified — across an index of 43,000+ MCP servers.