Slack bot gets 403 from sentry

I have some issue with slack’s integration. I think I followed correctly with integration docs, though.

I click on any button in slack (Resolve/Ignore) and I see that the slack bot gets 403 from the sentry’s app. Additionally, I see also nginx’s logs which explain more but I still don’t know what is the problem.

172.27.0.1 - - [22/Mar/2021:11:04:06 +0000] "POST //extensions/slack/action/ HTTP/1.0" 403 5630 "-" "Slackbot 1.0 (+https://api.slack.com/robots)" "3.238.104.54"
172.27.0.1 - - [22/Mar/2021:11:04:16 +0000] "POST //extensions/slack/action/ HTTP/1.0" 403 5630 "-" "Slackbot 1.0 (+https://api.slack.com/robots)" "3.239.192.72"