Custom fields for comments not working

I’m trying to add a custom input field to the comments form for my WP-theme.
I have tried different methods, but no one works. I don’t get any fields added to the comment sections. I have tried two different methods.
First this method:
https://wpengineer.com/2214/adding-input-fields-to-the-comment-form/

Secondly this method (both by installing as plugin and also by adding directly to functions-php):
https://www.smashingmagazine.com/2012/05/adding-custom-fields-in-wordpress-comment-form/#top

Does anyone have an Idea where I can begin to look for a fix?
Cheers.