It took about an hour for me to finally get this workflow to work as a non-technical user.
Just wanted to share some key pointers so others in a similar position can get this up and running asap:
Even as an existing paid ChatGPT WebUI user, after generating your API key, you need to set up payment to use the API needed for this workflow.
I had free credits which had already expired.
You can do so here: https://platform.openai.com/account/billing/overview
I used Homebrew to install the latest Python 3.11 and its dependencies.
This was not easy to figure out, and I followed this YouTube video: https://www.youtube.com/watch?v=6sJ0qKTyJnc
I suspect this Homebrew installation is not needed as some users above have mentioned it comes preinstalled with MacOS (or something like that).
This was not necessary (as mentioned by vitor in the next post).
Go to ~/Library/Application Support/Alfred/Workflow Data/ and open the file ChatFred_Error.log to self-solve problems easily.
There are other ways to troubleshoot as written by OP here: https://github.com/chrislemke/ChatFred/#troubleshooting-️ but I found reading this log file to be the most helpful.
The last hurdle I encountered was being presented with the error message The model: `gpt-4` does not exist.
After some research, I've found that it is required to enter a waitlist for access to the gpt-4 API: https://openai.com/waitlist/gpt-4-api
I will just use ChatGPT 3.5 in this workflow for the time being.