I've verified I get notifications on a public repository on my user account osowskit.
I've installed the Slack GitHub App to https://github.com/GH4B and selected two private repositories.

When running the command /github subscribe GH4B/pivatetest I get the following error:
Could not find resource: _GH4B/pivatetest_
I've tried the following:
I just ran into a similar problem and got around it by re-connecting my slack account to my github account.
@osowskit Could you try running /github signin to re-auth and then check if this problem persists?
Was this deployed? I wasn't able to subscribe to the same test rep after signing in again.
I can subscribe to the repo after /github signin

Could it be possible that the GitHub app user oauth access token doesn't have access to repos that were created after the token was issued?
Finally go to the bottom of this:
22:16:33.790Z DEBUG probot: GitHub request: GET /repos/:owner/:repo - 403 undefined
params: {
"owner": "GH4B",
"repo": "pivatetest",
"request": {
"rejectUnauthorized": true,
"timeout": 0
},
"baseUrl": "https://api.github.com"
}
22:16:33.790Z TRACE http: couldn't find repo (id=c2265398-9783-4ebc-9df9-c94af48ffcfa)
HttpError: {"message":"Resource protected by organization SAML enforcement. You must grant your personal token access to this organization.","documentation_url":"https://help.github.com/articles/authorizing-a-personal-access-token-for-use-with-a-saml-single-sign-on-organization"}
at IncomingMessage.response.on (/Users/bkeepers/projects/slack-app/node_modules/@octokit/rest/lib/request/request.js:73:18)
at IncomingMessage.emit (events.js:165:20)
at endReadableNT (_stream_readable.js:1101:12)
at process._tickCallback (internal/process/next_tick.js:152:19)
This request is being made with a user's access token that was gotten via GitHub Apps + OAuth.
@bkeepers I'm hitting this error too, with private repos on an org that has SAML turned on - all my tokens are SSO-enabled, so I'm not sure what's up with that...
Is this a bug with this integration or something on my side?
@hairyhenderson It looks like this is a bug with GitHub Apps. The team is working on it, but for now the integration won't work with any org that has SAML.
@bkeepers ok, thanks for the clarification! Will wait patiently, and continue to use the legacy GitHub app until it's fixed 馃檪
Hey guys, my team is seeing something similar, hoping to find out if its a symptom of this same bug. We (read: I) just installed the new GitHub App in our workspace, and this error message is popping up anytime I attempt to (re)subscribe to a repo from a Slack channel:

When I click the Install GitHub App button, I'm taken here:
https://github.com/apps/slack/installations/new/permissions?target_id=849935
^ which just displays the generic GitHub 404 page.
Note that our workspace does use SAML.
Thoughts?
Resource protected by organization SAML enforcement.
A fix for this was pushed out today (thanks @mtodd), so anyone who was having subscribing on organizations using SAML enforcement should be able to now. Let us know if you see any issues.
^ which just displays the generic GitHub 404 page.
@jpeterson I think you're actually running into #316.
I had the same issue but resolved it using "/github signin" to reconnect my GitHub account. Thanks to @wilhelmklopp
I'm seeing this with my org that uses SAML I connect the app and do a /github signin but any time I try to subscribe I get this:

would be great if this worked!
Most helpful comment
I just ran into a similar problem and got around it by re-connecting my slack account to my github account.
@osowskit Could you try running
/github signinto re-auth and then check if this problem persists?