I’m typing this out here in hopes that next time my own problems with this come up, this page could show up in my search. But it’s also out there for anyone else who stumbles on this page.
When typing a class lesson in LearnDash (could be a WordPress thing combineed with LD, I’m not sure) I kept getting a pink bar with the error:
Updating failed. The response is not a valid JSON response.
I tried EVERYTHING else. But finally realized the one thing that made THIS page different than others in the class I was typing up: it had a shareasale affiliate code in it. Shareasale provides a long scripty kind of code that made the site go nuts – I shortened it in Bitly and BOOM. Fixed.
Art nerds, unite.