Error when testing the Arduino Example?

Fairly new to WebThings.
I tried searching the borad for this first but didnt seem to hit upon anything.

I am trying to use JUST the example code as found on
I have added the webthing library to my arduino IDE libraries, and ArduinoJson was already there from prior projects, and it is up to date.

I copied and pasted the example code from into the IDE, entered a SSID and Password, saved it, clicked verify, and to my shock and horror saw a compilation error.

In file included from 

C:\Users\ME\Documents\Arduino\libraries\webthing-arduino/Thing.h:16:31: fatal 
error: ESPAsyncWebServer.h: No such file or directory

#include <ESPAsyncWebServer.h>


compilation terminated.

exit status 1
Error compiling for board LOLIN(WEMOS) D1 R2 & mini.

Is there something OTHER then the Webthing and ArduinoJson libraries that I should have downloaded that wasnt mentioned in the page?

The framework page identifies webthing-arduino is for PlatformIO and webthing is for ArduinoIDE. However when I went to add the library to ArduinoIDE the only result was for webthing-arduino which I installed (version 0.9.0).
Have the 2 libraries been merged?
Did I add the wrong library?
Should I uninstall and ALT+F4 life?

Thanks in advance

Per the README:

You will also need to download the ESP Async WebServer library and unpack it in your sketchbook’s libraries folder.