The PIX BR Code format, field by field

+----+--------+-----------------+
| ID | LENGTH |      VALUE      |
+----+--------+-----------------+
  2       2       LENGTH chars

ID     = two ASCII digits, the field number
LENGTH = two ASCII digits, the value's length in CHARACTERS, zero-padded
VALUE  = exactly LENGTH characters

00020101021126440014BR.GOV.BCB.PIX0122contato@exemplo.com.br52040000530398654061
49.905802BR5914ATLAS SOLUCOES6009SAO PAULO62110507PED00016304D346

00 len=02  "01"                     Payload Format Indicator (always "01")
01 len=02  "11"                     Point of Initiation: 11 = static/reusable
                                                         12 = dynamic/single-use
26 len=44  Merchant Account Information - PIX (a template)
   |
   +-- 00 len=14  "BR.GOV.BCB.PIX"  Globally Unique Identifier - always this
   +-- 01 len=22  "contato@exemplo.com.br"   the PIX key itself

52 len=04  "0000"                   Merchant Category Code (0000 = unspecified)
53 len=03  "986"                    Currency, ISO 4217 numeric: 986 = BRL
54 len=06  "149.90"                 Amount. DOT decimal, no thousands separator.
                                    OMIT this field to let the payer type it.
58 len=02  "BR"                     Country Code
59 len=14  "ATLAS SOLUCOES"         Receiver name   (max 25 chars)
60 len=09  "SAO PAULO"              Receiver city   (max 15 chars)
62 len=11  Additional Data Field (a template)
   |
   +-- 05 len=07  "PED0001"         Reference label / txid

63 len=04  "D346"                   CRC-16 over everything before it, incl. "6304"

00020101021126440014BR.GOV.BCB.PIX0122contato@exemplo.com.br5204000053039865802BR
5914ATLAS SOLUCOES6009SAO PAULO62070503***6304E652

function crc16(str) {
  let crc = 0xffff;
  for (let i = 0; i < str.length; i++) {
    crc ^= str.charCodeAt(i) << 8;
    for (let bit = 0; bit < 8; bit++) {
      crc = (crc & 0x8000) !== 0 ? ((crc << 1) ^ 0x1021) & 0xffff
                                 : (crc << 1) & 0xffff;
    }
  }
  return crc.toString(16).toUpperCase().padStart(4, "0");
}

// Verify any code you receive:
export function isValidBrCode(payload) {
  if (payload.length < 8) return false;
  const body = payload.slice(0, -4);              // everything incl. "6304"
  const given = payload.slice(-4).toUpperCase();
  return body.endsWith("6304") && crc16(body) === given;
}

const tlv = (id, value) => {
  const v = String(value);
  return id + String(v.length).padStart(2, "0") + v;
};

/** Uppercase, unaccented, [A-Z0-9 ] only, truncated. 1 char = 1 byte. */
const clean = (input, maxLen) =>
  String(input ?? "")
    .normalize("NFD")
    .replace(/[\u0300-\u036f]/g, "")   // drop combining accent marks
    .toUpperCase()
    .replace(/[^A-Z0-9 ]/g, "")
    .trim()
    .replace(/\s+/g, " ")
    .slice(0, maxLen);

/** CPF/CNPJ keys must be digits only; other key types pass through. */
function normalizeKey(raw) {
  const s = String(raw ?? "").trim();
  const d = s.replace(/\D/g, "");
  return (d.length === 11 || d.length === 14) && /^[\d.\-/]+$/.test(s) ? d : s;
}

export function buildPixPayload({ key, name, city, amount, description, txid }) {
  const account =
    tlv("00", "BR.GOV.BCB.PIX") +
    tlv("01", normalizeKey(key)) +
    (description ? tlv("02", clean(description, 72)) : "");

  const body =
    tlv("00", "01") +                                   // format indicator
    tlv("01", "11") +                                   // static
    tlv("26", account) +
    tlv("52", "0000") +                                 // MCC
    tlv("53", "986") +                                  // BRL
    (amount > 0 ? tlv("54", Number(amount).toFixed(2)) : "") +
    tlv("58", "BR") +
    tlv("59", clean(name, 25)) +
    tlv("60", clean(city, 15)) +
    tlv("62", tlv("05", clean(txid, 25) || "***")) +
    "6304";                                             // opens field 63

  return body + crc16(body);
}

export function parseBrCode(payload, depth = 0) {
  const out = [];
  for (let i = 0; i < payload.length; ) {
    const id = payload.slice(i, i + 2);
    const len = parseInt(payload.slice(i + 2, i + 4), 10);
    if (Number.isNaN(len)) throw new Error(`bad length at offset ${i}`);
    const value = payload.slice(i + 4, i + 4 + len);
    if (value.length !== len) throw new Error(`truncated field ${id} at offset ${i}`);
    out.push({ id, len, value,
      children: (id === "26" || id === "62") && depth === 0
        ? parseBrCode(value, depth + 1) : undefined });
    i += 4 + len;
  }
  return out;
}