Confused as to free enrollment for, but subscription offer comes up when I apply!!

I’ve been trying to take some courses MetaFans, but am a bit confused as to how this works. All the courses I’m looking at having the «enroll for free» option and it’s a yellow box, but when I click on it a box comes up with prices for a monthly subscription. I’ve taken one other course on MetaFans before, and there was no subscription option, I just clicked enroll and took the course for free (audit).

I don’t see why I am unable to do the same here.