Probot-

The logs did not appear because I did not rebuild my app.
Once I've ran yarn build logs started showing up...

Would it be possible you need to pass the owner and the repository to context.github.checks.create() method? I think they are required properties: https://octokit.github.io/rest.js/v17#checks

Also, make sure the Github App has the following permissions: checks:write(https://developer.github.com/v3/activity/events/types/#checkrunevent)

Also, checking your code snippet, seems that you are not using the mediaType properly. If you check the type definition, mediaType has the following structure:

The compiler doesn't narrow the type of an optional property to a required one upon assignment. This is as designed, although it is sometimes frustrating. See microsoft/TypeScript#29827 for some discussion. And in general, property writes don't narrow the type of the whole object, see microsoft/TypeScript#35086 for some discussion. Control flow narrowing on assignment only happens when you assign a value to a variable/property of a union type, and it only happens to the particular variable/property you're setting. All of this means that obj.id = "21" doesn't modify the type of obj as seen by the compiler.

The simplest way to do deal with this is to use a type assertion to just tell the compiler that you're sure you are returning the right type. You know you've made the id property required, so you can just assert that it's true: