ESPAsyncWiFiManager/examples/ModelessConnect/ModelessConnect.ino

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

//needed for library
#include <DNSServer.h>
#include <ESPAsyncWebServer.h>
#include <ESPAsyncWiFiManager.h>         //https://github.com/tzapu/WiFiManager

AsyncWebServer server(80);
DNSServer dns;
AsyncWiFiManager wifiManager(&server,&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
    //reset saved settings
    //wifiManager.resetSettings();

    //set custom ip for portal
    //wifiManager.setAPConfig(IPAddress(10,0,1,1), IPAddress(10,0,1,1), IPAddress(255,255,255,0));

    //fetches ssid and pass from eeprom 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
    //wifiManager.autoConnect("AutoConnectAP");
    //or use this for auto generated name ESP + ChipID
    //wifiManager.autoConnect();
    wifiManager.startConfigPortalModeless("ModelessAP", "Password");


 server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
    request->send(200, "text/plain", "Hello World");
  });

}

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