I have some problems connecting Arduino to Ecobee using Ecobee API

I am trying to connect my Arduino Uno Wifi to the Ecobee so that I can control temperatures. The link to the original Arduino project is here. The code that I am running requires a developer client id and I'm not sure where it is. I looked through the Ecobee example page as it mentions client id but does not directly state what the client id is. Where exactly is it? Although I have correctly found my access token, refresh token, and code, and ecobee Pin and authorized the application in the "My Apps" section, when I run the code, this message pops up:

Error in obtaining access code, need to run create_new_refresh_keys()

ecobeePin Status code: -3

Refresh Response:

deserializeJson() failed with code EmptyInput

I am completely stuck here and not sure how to move on forward. Any help will be appreciated!