I have been working with API here for a couple weeks and got it to work for my project yesterday.
I am not sure why you are not able to retrieve the sermon meta data.
This is the post that helped me some what figure out how to use the API.
https://ww.wp.xz.cn/support/topic/rest-api-33/
I was able to perform a GET Request on https://mychurchdomain.com/wp-json/wp/v2/wpfc_sermon/ and I received the JSON in the body of the request. I easily test this functionality by putting the url in my browser and was able to see the JSON text.
Are you getting any HTTP response error codes?
The reason I ask is I was originally getting a 403 when I started trying to access the API programmatically. I later found out that this was because of some anti-bot security that my website host had on their side. Once I included a valid User-Agent in my HTTP GET request header then I was able to pull the data.
Hope this helps!
