How to edit teleport.<example.com>/appID

I read the document and found if we have several facets we need to point the appid url to a json file.

My question is how to do it?
while I curl teleport.<example.com>/appID it return 404.
where should I store the json file?

For U2F facets list you can look here:

https://gravitational.com/teleport/docs/admin-guide/

But I’m not sure what do you mean by JSON file, can you elaborate on that?