public static @NotNull ByteBuffer generateCustom(int payloadLength, @NotNull Random random) {
    ByteBuffer byteBuffer = ByteBuffer.allocate(TIMESTAMP_LENGTH + payloadLength);

    long utc = ZonedDateTime.now(ZoneOffset.UTC).toInstant().toEpochMilli() / 1000;
    int timestamp = (int)(utc - EPOCH);
    byteBuffer.putInt(timestamp);

    byte[] bytes = new byte[payloadLength];
    random.nextBytes(bytes);
    byteBuffer.put(bytes);
    return byteBuffer;
  }
public static @NotNull ByteBuffer generateCustom(int payloadLength, @NotNull Random random)