TestCafe using --ssl command throws Mac verify failure error

When I run the following command testcafe --ssl pfx=path/to/file.pfx safari mytestfile.js, I always immediately get a mac verify failure error message in the terminal window.

I created my .pfx file using openssl req -x509 -newkey rsa:2048 -keyout key.pem -out cert.pem -days 999999 -nodes

Questions:

• Am I using the wrong .pfx file?
• What is causing this error?
• How would I go about fixing this issue?

I have tried using the instructions here (https://devexpress.github.io/testcafe/documentation/using-testcafe/programming-interface/createtestcafe.html), but even that doesn't work.

Any help would be greatly appreciated! :)