In order to validate the Slack connection successfully and also for consuming and subscribing messages from there, the necessary `Bot Token Scopes` should be set in the customer Slack app. (I found some information about scopes here: https://camel.apache.org/components/3.13.x/slack-component.html#_consumer (I didn't find any information in version 2.x)
That scopes should be mentioned in Prerequisite section https://access.redhat.com/documentation/en-us/red_hat_fuse/7.9/html/connecting_fuse_online_to_applications_and_services/connecting-to-slack_connectors#creating-slack-connections_slack