Funny,
I was looking at this just yesterday again. I think I have found someone that has done this now ( see
https://imperativeideas.com/making-custom-fields-work-yoast-wordpress-seo/ ) I’ve tried it, and seems to be almost working. I say almost as the check still shows the focus keyword(s) not to be in the content on the traffic light system, even though it does find them in there to pass it.
Try it, it will make more sense than I have just made here.
