A payment gateway for MCP servers, and the security bugs I found in my own code first

Fewer than 5% of MCP servers make money. I put a real payment gate in front of one and wrote down what actually broke. The problem, with numbers There are 10,000+ Model Context Protocol (MCP) servers out there right now, with 97 million+ combined downloads. MCP is the emerging standard for how AI agents call tools — search, databases, APIs, whatever a server wants to expose. It's had a huge adoption wave. Fewer than 5% of the people running those servers earn anything from them. Not because nobody would pay. It's because "let people pay per call" means building, from scratch, on top of your actual product: an HTTP 402 challenge/response flow signature verification for the payment authorization (real cryptographic recovery, not just "is there a signature-shaped string present") settlement against a payment facilitator replay protection (nobody should be able to reuse the same signed payment twice) revenue accounting per caller, per tool, per owner None of that has an