Below is the updated version from the example library. It works on both ESPs (32 and 8266).
@Toro_Blanco check lines 24 and 108. There’s a difference with the number of array between the old and new version.
char blynk_token[33] = "YOUR_BLYNK_TOKEN";
....
WiFiManagerParameter custom_blynk_token("blynk", "blynk token", blynk_token, 34);
I recall reading somewhere that the second line array number should be one number less than the one defined on the first line just as shown with the old code. However, the new code it’s the other way around. Needless, both codes work 
And what’s the use of a delay after a ESP.reset()?
#include <FS.h> //this needs to be first, or it all crashes and burns...
#if defined(ESP8266)
#include <ESP8266WiFi.h> //https://github.com/esp8266/Arduino
#else
#include <WiFi.h> //https://github.com/esp8266/Arduino
#endif
//needed for library
#include <DNSServer.h>
#if defined(ESP8266)
#include <ESP8266WebServer.h>
#else
#include <WebServer.h>
#endif
#include <WiFiManager.h> //https://github.com/tzapu/WiFiManager
#include <ArduinoJson.h> //https://github.com/bblanchon/ArduinoJson
//define your default values here, if there are different values in config.json, they are overwritten.
//length should be max size + 1
char mqtt_server[40];
char mqtt_port[6] = "8080";
char blynk_token[33] = "YOUR_BLYNK_TOKEN";
//default custom static IP
char static_ip[16] = "10.0.1.56";
char static_gw[16] = "10.0.1.1";
char static_sn[16] = "255.255.255.0";
//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 setup() {
// put your setup code here, to run once:
Serial.begin(115200);
Serial.println();
//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);
DynamicJsonBuffer jsonBuffer;
JsonObject& json = jsonBuffer.parseObject(buf.get());
json.printTo(Serial);
if (json.success()) {
Serial.println("\nparsed json");
strcpy(mqtt_server, json["mqtt_server"]);
strcpy(mqtt_port, json["mqtt_port"]);
strcpy(blynk_token, json["blynk_token"]);
if(json["ip"]) {
Serial.println("setting custom ip from config");
//static_ip = json["ip"];
strcpy(static_ip, json["ip"]);
strcpy(static_gw, json["gateway"]);
strcpy(static_sn, json["subnet"]);
//strcat(static_ip, json["ip"]);
//static_gw = json["gateway"];
//static_sn = json["subnet"];
Serial.println(static_ip);
/* Serial.println("converting ip");
IPAddress ip = ipFromCharArray(static_ip);
Serial.println(ip);*/
} else {
Serial.println("no custom ip in config");
}
} else {
Serial.println("failed to load json config");
}
}
}
} else {
Serial.println("failed to mount FS");
}
//end read
Serial.println(static_ip);
Serial.println(blynk_token);
Serial.println(mqtt_server);
// 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_mqtt_port("port", "mqtt port", mqtt_port, 5);
WiFiManagerParameter custom_blynk_token("blynk", "blynk token", blynk_token, 34);
//WiFiManager
//Local intialization. Once its business is done, there is no need to keep it around
WiFiManager wifiManager;
//set config save notify callback
wifiManager.setSaveConfigCallback(saveConfigCallback);
//set static ip
IPAddress _ip,_gw,_sn;
_ip.fromString(static_ip);
_gw.fromString(static_gw);
_sn.fromString(static_sn);
wifiManager.setSTAStaticIPConfig(_ip, _gw, _sn);
//add all your parameters here
wifiManager.addParameter(&custom_mqtt_server);
wifiManager.addParameter(&custom_mqtt_port);
wifiManager.addParameter(&custom_blynk_token);
//reset settings - for testing
//wifiManager.resetSettings();
//set minimu quality of signal so it ignores AP's under that quality
//defaults to 8%
wifiManager.setMinimumSignalQuality();
//sets timeout until configuration portal gets turned off
//useful to make it all retry or go to sleep
//in seconds
//wifiManager.setTimeout(120);
//fetches ssid and pass and tries to connect
//if it does not connect it starts an access point with the specified name
//here "AutoConnectAP"
//and goes into a blocking loop awaiting configuration
if (!wifiManager.autoConnect("AutoConnectAP", "password")) {
Serial.println("failed to connect and hit timeout");
delay(3000);
//reset and try again, or maybe put it to deep sleep
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(mqtt_port, custom_mqtt_port.getValue());
strcpy(blynk_token, custom_blynk_token.getValue());
//save the custom parameters to FS
if (shouldSaveConfig) {
Serial.println("saving config");
DynamicJsonBuffer jsonBuffer;
JsonObject& json = jsonBuffer.createObject();
json["mqtt_server"] = mqtt_server;
json["mqtt_port"] = mqtt_port;
json["blynk_token"] = blynk_token;
json["ip"] = WiFi.localIP().toString();
json["gateway"] = WiFi.gatewayIP().toString();
json["subnet"] = WiFi.subnetMask().toString();
File configFile = SPIFFS.open("/config.json", "w");
if (!configFile) {
Serial.println("failed to open config file for writing");
}
json.prettyPrintTo(Serial);
json.printTo(configFile);
configFile.close();
//end save
}
Serial.println("local ip");
Serial.println(WiFi.localIP());
Serial.println(WiFi.gatewayIP());
Serial.println(WiFi.subnetMask());
}
void loop() {}
Here is the new library.
