[x402] Add native fiat currency support

I've been running an MCP server for ad campaign intelligence called [Adpulse ](https://adpulse.fyi/)for a few months — audit tools, copy generation, competitor research, that kind of thing. Agents call it autonomously, mostly through Claude. When I needed to monetize, x402 felt like the obvious choice. HTTP-native pay-per-call, no accounts, designed exactly for this. I spent two weekends implementing it. Six weeks later I ripped it out. Here's the honest breakdown. **The protocol is genuinely elegant** The handshake is clean: client hits endpoint → gets `402` → agent signs transaction → retries. For pure agent-to-agent billing with no human in the loop, it's the right primitive. app.post('/mcp/tools/:tool', async (req, res) => { const verified = await verifyPayment(req.headers['x-payment']); if (!verified.valid) return res.status(402).json({ error: 'Payment required' }); const result = await runTool(req.params.tool, req.body); res.json(result); }); That's what I thought I was shipping. It was not what I shipped. # What I didn't expect: I was building a payments company x402 handles the transaction handshake. Everything else is on you. My "quick monetization weekend" turned into: * Separate payment gates per tool type (research vs. copy gen vs. audit all needed different pricing logic) * Payment retries when agents failed mid-transaction and jobs were left in limbo * Auth middleware from scratch * Rate limiting per wallet * Refund logic for when a tool errored *after* payment cleared * Debugging silent webhook failures * KYC paperwork just to get settlements moving And then the one I genuinely didn't see coming: some agents hitting my API only transacted in USD. Not USDC. Not ETH. **Plain dollar billing.** Vanilla x402 had no answer for that — I'd need an entirely separate billing path running in parallel. That's when I had to ask myself: am I building an ad intelligence tool or a payment infrastructure company? **What I moved to instead** I ended up using a [credit wallet proxy](http://bit.ly/4s0Ny3I) — users buy a bundle upfront, calls draw down against it. Supports both crypto and fiat out of the box. Deleted around 300 lines of payment code. The MCP config change was a single URL swap. I'm not going to name the specific service here since that's not really the point of this post — happy to share in comments if anyone's curious. The broader point is: the *model* (prepaid wallet vs. per-call crypto) solved my user problem in a way x402 couldn't yet. https://preview.redd.it/esllo0n2p8og1.png?width=914&format=png&auto=webp&s=f020227f3d3909e61174e94c1f85169102710256 # Curious where others have landed — anyone solved the fiat + crypto dual-stack problem cleanly? And if you're building monetized MCP servers, what payment layer are you actually using in production? #