Hi.
They recently changed the interface.
I’m currently working on updating the eBook and I’m testing all projects from start and updating them to the latest versions of the libraries and ESP32 core.
 
TO FIX THE ISSUE:
You need to create an app first before getting access to the API key.
 
At the bottom of that page, click on the </> icon to create a web app.
 

1. Give a name to your app. For example “ESP IOT App”. Select Also set up Firebase Hosting. Click on Register App.
2. In the next section, a code snipet will show up. In the firebaseConfig variable, you can see the apiKey. Copy the API key. Then, click Next.
3. Click Next-
4. Continue to the Console

 
Now, you can see that on your project setting page, you have the firebaseConfig variable with the API key.
 
Let me know if you can get the API key.

Now, you don’t need to follow section 4) on page 128 because we already did it here.
 
Regards,
Sara