I think you need to update the setting’s screenshots maybe they have been changed.

I habe problems to connect from WP Tools Slack Alert to Slack: error returned ‘invalid_auth’. I checked and rechecked the requested ‘Slack App Token’.
Slack changed the login rules, even for classic slack apps. Are there any plans to update WP Down Slack Alert to the changed SLACK rules ? see link https://api.slack.com/changelog/2020-11-no-more-tokens-in-querystrings-for-newly-created-apps