Pull that project
Than open directory "backend" and type in terminal "npm start"
Than open directory "frontend" and type in terminal "npm start"
Open in your browser localhost:3000/
Past in input test email - testingapis@hubspot.com
Tap "Send" button and wait for result

Info:
backend PORT: 5000
frontend PORT: 3000

Link to second answer:
https://ibb.co/J7M51QY