Generate a QR code or barcode as an image (SVG or PNG). Symbologies: qrcode/qr, code128, code39, ean13, ean8, upca, upce, isbn10, isbn13, issn, itf, gs1-128, databar.
Without payment, the server returns 402 Payment Required with x402 challenge details.
A paying agent signs a USDC transaction on Base and retries with the payment header.