Default paywall price discrepency

[jamesbachini]

The default paywall that displays pricing seems to be a decimal out (see screenshot attached)

I've isolated this down to the simplest possible implementation:

Code to reproduce

import express from "express";
import { paymentMiddlewareFromConfig } from "@x402/express";
import { HTTPFacilitatorClient } from "@x402/core/server";
import { ExactStellarScheme } from "@x402/stellar/exact/server";

const NETWORK = "stellar:testnet";
const FACILITATOR_URL = "https://www.x402.org/facilitator";
const PAY_TO = "G...YOURADDRESS...";
const app = express();

app.use(
  paymentMiddlewareFromConfig(
    {
      [`GET /my-service`]: {
        accepts: {
          scheme: "exact",
          price: "$0.51", // price in USDC
          network: NETWORK,
          payTo: PAY_TO,
        },
      },
    },
    new HTTPFacilitatorClient({ url: FACILITATOR_URL }),
    [{ network: NETWORK, server: new ExactStellarScheme() }],
  ),
);
app.get("/my-service", (_, res) => res.json({ secret: "valuable content" }));

app.listen(3003);

[jamesbachini]

Checked a few different values and types:

"$0.51", "0.52", 0.53, Number(0.54)

All have the same issue

[cryptomotifs]

The decimal-out symptom is almost always an atomic-unit vs. display-unit mismatch, and Stellar makes this extra sharp because native Stellar assets use 7 decimals (stroop = 10⁻⁷), not the 6 decimals that USDC uses on EVM chains.

Two places to check in @x402/stellar:

1. ExactStellarScheme.buildPaymentRequirements() — if it reads price: "$0.51" as a float and multiplies by 10**6 (copied from the EVM scheme), then divides by 10**7 in the paywall formatter, you'd get the exact "off by one decimal" you're seeing (displays $0.051 instead of $0.51, or $5.10 if the inverse is wrong).

2. The paywall HTML template itself — @x402/paywall currently reads maxAmountRequired in atomic units and formats with a hard-coded decimals lookup per (network, asset). If the Stellar USDC entry is missing from that table it falls back to 6, producing the same off-by-one.

Quick diagnostic: hit the route with curl -i and inspect the raw 402 body:

curl -i http://localhost:3003/my-service
# look at accepts[0].maxAmountRequired + asset.decimals

If maxAmountRequired is 5100000 and asset.decimals is 7, the server is correct and the paywall HTML is dividing by 10**6 — bug in @x402/paywall. If it's 510000 or 51000000, the scheme's parser rounded wrong.

The asset-decimals table is worth asserting regardless; Stellar USDC issued by centre.io publishes decimals=7 on GET /.well-known/stellar.toml, which the scheme should pull at startup rather than hard-code.