Task: Post a message in a Slack channel

n8n workflow JSON:
{"id":"8","name":"slack-workflow","nodes":[{"name":"On clicking 'execute'","type":"n8n-nodes-base.manualTrigger","position":[250,300],"parameters":{},"typeVersion":1},{"name":"Slack","type":"n8n-nodes-base.slack","position":[410,300],"parameters":{"text":"This is an example.","channel":"example-channel","blocksUi":{"blocksValues":[]},"attachments":[],"otherOptions":{},"authentication":"oAuth2"},"credentials":{"slackOAuth2Api":"slack2-oauth2-docker-ivov"},"typeVersion":1}],"active":false,"settings":{},"connections":{"On clicking 'execute'":{"main":[[{"node":"Slack","type":"main","index":0}]]}}}