Receiving garbage value when sending a Json object from Arduino Uno to NodeMCU using SoftwareSerial
The problem with ArduinoJson.h is that it doesn't ensure robust and reliable transfer over UART serial.

Instead, you should use SerialTransfer.h to automatically packetize and parse your data for inter-Arduino communication without the headace.The library is installable through the Arduino IDE and includes many examples.

Here are the library's features:


  This library:
  
  
  can be downloaded via the Arduino IDE's Libraries Manager (search "SerialTransfer.h")
  works with "software-serial" libraries
  is non blocking
  uses packet delimiters
  uses consistent overhead byte stuffing
  uses CRC-8 (Polynomial 0x9B with lookup table)
  allows the use of dynamically sized packets (packets can have payload lengths anywhere from 1 to 254 bytes)
  can transfer bytes, ints, floats, and even structs!!
  


Example TX Arduino Sketch:

#include "SerialTransfer.h"

SerialTransfer myTransfer;

void setup()
{
  Serial.begin(115200);
  Serial1.begin(115200);
  myTransfer.begin(Serial1);
}

void loop()
{
  char buff[] = "hi";

  myTransfer.txObj(buff, sizeof(buff));
  myTransfer.sendData(sizeof(buff));
  delay(100);
}


Example RX Arduino Sketch:

#include "SerialTransfer.h"

SerialTransfer myTransfer;

void setup()
{
  Serial.begin(115200);
  Serial1.begin(115200);
  myTransfer.begin(Serial1);
}

void loop()
{
  if(myTransfer.available())
  {
    char buff[40];
    
    myTransfer.rxObj(buff, sizeof(buff));
    
    Serial.println("New Data: ");
    Serial.write(buff, sizeof(buff));
    Serial.println();
  }
  else if(myTransfer.status &lt; 0)
  {
    Serial.print("ERROR: ");

    if(myTransfer.status == -1)
      Serial.println(F("CRC_ERROR"));
    else if(myTransfer.status == -2)
      Serial.println(F("PAYLOAD_ERROR"));
    else if(myTransfer.status == -3)
      Serial.println(F("STOP_BYTE_ERROR"));
  }
}