How do I enable chapters with Podlove stand alone Wordpress player?

I’ve looked everywhere, but I can’t figure out how to enable Chapters on the Podlove stand alone player for Wordpress.

I’ve read the instructions here:

But this confuses me: "Takes chapter json string from the defined custom field (the standard WordPress ones) "

How do I do that? What is the “defined custom field”?

Just to be clear, I don’t want to use the Podlove Publisher for technical reasons on my application. I just need to have chapters on the stand alone player for Wordpress.

Thanks in advance.