Appointments+ Google "Key File Does Not Exist"

I'm looking for some help syncing Appointments+ with Google. I followed the video tutorial as closely as I could but it was created in 2013 and the Google Developers Console is much different now.

Specifically, I believe my error is happening between steps 5-11. And yes, I'm placing the key file in the correct location on the server. Oddly, the file download does not have an extension and simply downloads as Unknown so I renamed it to "privatekey." I've attached it here.

Thanks in advance for looking into this.