ESPAsyncWiFiManager/examples/AutoConnectWithFeedback/AutoConnectWithFeedback.ino

#if defined(ESP8266)
#include <ESP8266WiFi.h>                 //https://github.com/esp8266/Arduino
#else
#include <WiFi.h>
#endif

//needed for library
#include <ESPAsyncDNSServer.h>           //https://github.com/devyte/ESPAsyncDNSServer
                                         //https://github.com/me-no-dev/ESPAsyncUDP
#include <ESPAsyncWebServer.h>
#include <ESPAsyncWiFiManager.h>         //https://github.com/tzapu/WiFiManager

void configModeCallback (AsyncWiFiManager *myWiFiManager) {
  Serial.println("Entered config mode");
  Serial.println(WiFi.softAPIP());
  //if you used auto generated SSID, print it
  Serial.println(myWiFiManager->getConfigPortalSSID());
}

AsyncWebServer server(80);
AsyncDNSServer dns;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);

  //WiFiManager
  //Local intialization. Once its business is done, there is no need to keep it around
  AsyncWiFiManager wifiManager(&server,&dns);
  //reset settings - for testing
  //wifiManager.resetSettings();

  //set callback that gets called when connecting to previous WiFi fails, and enters Access Point mode
  wifiManager.setAPCallback(configModeCallback);

  //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()) {
    Serial.println("failed to connect and hit timeout");
    //reset and try again, or maybe put it to deep sleep
    ESP.reset();
    delay(1000);
  }

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

}

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

}