How I let AI agents pay for APIs per call (the HTTP 402 path) (opens in new tab)

If you've built an MCP server or any API that costs you money to run (an LLM call, a paid data source, compute), you've probably hit the same wall I did: How do you get paid per call — when the caller is an AI agent, not a human with a credit card form? A human can sign up, enter a card, get an API key. An autonomous agent can't fill out a Stripe checkout form mid-task. And you don't want to hand an agent a raw API key with no spending limit — one runaway loop and your bill explodes. This pos...