You would have to provide a lot more information about your setup: for example, the REST API user that you've allocated needs to be able to create Custom Activities, and you have to separately prove that the Munchkin session is associated with a known lead in your Marketo database.
If you believe the API connection is itself functional, then you should talk to Wistia and ask them if they've been posting data.
IMO there's little to be gained from such indirect integrations as you can do the same thing with the JS API + Munchkin API, though without such friendly Custom Activity text (though much, much more scalable).
Thanks for the reply. The API was setup prior to my arrival here, and we have 9 previous videos that worked correctly. I used inspect element to ensure Munchkin was calling back without errors when I did my testing.
I will reach out to Wistia support to see if they can help.
Thank you very much!