PayPerFax explains MCP payment design that survives client retries
ediblesites · reddit · 2026-11-13
The maker of PayPerFax, a pay-per-fax MCP service, explains how they handle paid write tools when AI clients may retry after timeouts: createfax only creates an unpaid draft and returns a public web link where the human reviews the rendered fax, verifies the destination number and price, and pays in the browser — payment triggers the send. Retries just create more unpaid drafts (no dedup), so a retry can never trigger a second paid send. The tool description instructs the model to fetch agency fax numbers from official sites and show the source, and the preview displays the number before paying. Requiring a human to pay also rules out unattended batch jobs. Server: fax.payperfax.com/mcp (Streamable HTTP, no auth).
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