{"mensaje":"Este endpoint requiere POST con JSON, ej: {\"mensaje\":\"example.com wants you to sign in with your Ethereum account:\\n0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf\\n\\nSign in\\n\\nURI: https://example.com\\nVersion: 1\\nChain ID: 8453\\nNonce: abc12345\\nIssued At: 2026-10-02T20:00:00Z\",\"firma\":\"0xcc7863e87c5879d5fd0bb7b2bc925ec0f86f59a07badb05d8faffec9b061d18a6227988b56b1e18b7a0603d034a7c5b378f5b039e0af9c929bf090ded43dd5941c\"}. Precio: $0.003 USDC (Solana o Base)."}