There is no documentation about it - looks like they don’t like it if you host sentry on your own - but there is a forum post that helped me to fix Slack: How to configure Slack in your on-prem Sentry
There is no documentation about it - looks like they don’t like it if you host sentry on your own - but there is a forum post that helped me to fix Slack: How to configure Slack in your on-prem Sentry