I don't get a message from the GitHub Slack app.

[apt-mcjeon]

I installed the GitHub app on Slack.
I send pull request from GitHub, but I don't get any message in Slack.
Subscribe was done according to the manual.

1. I was receiving the message well on channel A.
2. I removed the GitHub app on channel A and registered the GitHub app on channel B.
3. I received all the messages well on channel A, but since I moved to channel B, only push messages are coming.