I’m experiencing the same thing here.
Same message from github web page when I try to setup a scheduled reminder to a private Slack channel:
The channel (...) was not found.
Check that it exists and that @github has been invited to it
Github APP has been added to the Slack channel
GitHubAPP was added to this conversation by O.G.
I can see the following help message when Slacking
/github on the said channel:
GitHub APP :wave: Need some help with /github?
Subscribe to notifications for a repository:
/github subscribe owner/repository
Unsubscribe from notifications for a repository:
/github unsubscribe owner/repository
Subscribe to notifications for all repositories in an organization:
/github subscribe owner
Unsubscribe from notifications for an organization:
/github unsubscribe owner
Subscribe to additional features and adjust the configuration of your subscription (Learn more):
/github subscribe owner/repository reviews,comments