Dear Sir/Madam,
I have upgraded the WiFi Manager Autoconnect with custom parameters to work with ArduinoJson 6. However, the custom parameters do not retain after the reset otherwise work as expected. I doubly ensured that I haven’t uncommented the
//wm.resetSettings();. 
I am struggling for a long. One year back I had the same issue question on Arduino Forum [https://forum.arduino.cc/t/wifi-manager-custom-parameters-are-not-saved-in-memory-via-ondemand-portal/921063/5]
I have hope from this forum. Kindly pinpoint where I go wrong. 
 

#include <FS.h>          // this needs to be first, or it all crashes and burns…
#include <WiFiManager.h> // https://github.com/tzapu/WiFiManager
#include <ArduinoJson.h> // https://github.com/bblanchon/ArduinoJson

#ifdef ESP32
  #include <SPIFFS.h>
#endif

//define your default values here, if there are different values in config.json, they are overwritten.

char telegram_token[50] = “YOUR_TELEGRAM_TOKEN”;
char chat_id[15]  = “UrChatID”;

//flag for saving data
bool shouldSaveConfig = false;

//callback notifying us of the need to save config
void saveConfigCallback () {
  Serial.println(“Should save config”);
  shouldSaveConfig = true;
}

void setupSpiffs(){
  //clean FS, for testing
  // SPIFFS.format();

  //read configuration from FS json
  Serial.println(“mounting FS…”);

  if (SPIFFS.begin()) {
    Serial.println(“mounted file system”);
    if (SPIFFS.exists(“/config.json”)) {
      //file exists, reading and loading
      Serial.println(“reading config file”);
      File configFile = SPIFFS.open(“/config.json”, “r”);
      if (configFile) {
        Serial.println(“opened config file”);
        size_t size = configFile.size();
        // Allocate a buffer to store contents of the file.
        std::unique_ptr<char[]> buf(new char[size]);

        configFile.readBytes(buf.get(), size);
        DynamicJsonDocument json(1024); //json(ESP.getMaxFreeBlockSize());
        DeserializationError error = deserializeJson(json,buf.get());
        //JsonObject& json = jsonBuffer.parseObject();
        //json.printTo(Serial);
        serializeJson(json,Serial);
        if (!error) {
          Serial.println(“\nparsed json”);

          //strcpy(mqtt_server, json[“mqtt_server”]);
            strcpy(telegram_token, json[“telegram_token”]);
            strcpy(chat_id, json[“chat_id”]);            
   
        } else {
          Serial.println(“failed to load json config”);
        }
      }
    }
  } else {
    Serial.println(“failed to mount FS”);
  }
  //end read
}

void setup() {
  WiFi.mode(WIFI_STA); // explicitly set mode, esp defaults to STA+AP  
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println();

  setupSpiffs();

  // WiFiManager, Local intialization. Once its business is done, there is no need to keep it around
  WiFiManager wm;

  //set config save notify callback
  wm.setSaveConfigCallback(saveConfigCallback);

  // setup custom parameters
  //
  // The extra parameters to be configured (can be either global or just in the setup)
  // After connecting, parameter.getValue() will get you the configured value
  // id/name placeholder/prompt default length
  //WiFiManagerParameter custom_mqtt_server(“server”, “mqtt server”, mqtt_server, 40);
  WiFiManagerParameter custom_telegram_token(“token”, “telegram token”, telegram_token, 50);
  WiFiManagerParameter custom_chat_id(“Chat_ID”, “chat_id”, chat_id, 15);
 

  //add all your parameters here
  //wm.addParameter(&custom_mqtt_server);
  wm.addParameter(&custom_telegram_token);
  wm.addParameter(&custom_chat_id);

  //reset settings – wipe credentials for testing
  //wm.resetSettings();

  //automatically connect using saved credentials if they exist
  //If connection fails it starts an access point with the specified name
  //here  “AutoConnectAP” if empty will auto generate basedcon chipid, if password is blank it will be anonymous
  //and goes into a blocking loop awaiting configuration
  if (!wm.autoConnect(“AutoConnectAP”, “password”)) {
    Serial.println(“failed to connect and hit timeout”);
    delay(3000);
    // if we still have not connected restart and try all over again
    ESP.restart();
    delay(5000);
  }

  //if you get here you have connected to the WiFi
  Serial.println(“connected…yeey :)”);

  //read updated parameters
  // strcpy(mqtt_server, custom_mqtt_server.getValue());
  strcpy(telegram_token, custom_telegram_token.getValue());
  strcpy(chat_id, custom_chat_id.getValue());
 

  //save the custom parameters to FS
  if (shouldSaveConfig) {
    Serial.println(“saving config”);
    DynamicJsonDocument json(1024); //json(ESP.getMaxFreeBlockSize());
    //JsonObject& json = jsonBuffer.createObject();
    // json[“mqtt_server”] = mqtt_server;
    json[“telegram_token”] = telegram_token;
    json[“chat_id”] = chat_id;
   
    File configFile = SPIFFS.open(“/config.json”, “w”);
    if (!configFile) {
      Serial.println(“failed to open config file for writing”);
    }
    serializeJsonPretty(json,Serial);
    //json.prettyPrintTo(Serial);
    serializeJson(json,configFile);
    //json.printTo(configFile);
    configFile.close();
    //end save
    shouldSaveConfig = false;
  }

}

void loop() {
  // put your main code here, to run repeatedly:

}