Slack uses Socket Mode, which means your bot connects outward to Slack's servers. No public URL or webhook endpoint needed.
Create a new Slack App from the Slack API dashboard. You need 2 tokens: an App-Level Token (starts with xapp-) for the socket connection, and a Bot Token (starts with xoxb-) for sending messages.
Your config file needs both:
{
"platform": "slack",
"appToken": "xapp-...",
"botToken": "xoxb-..."
}
Save as ~/.openclaw/platforms/slack.json and restart the daemon. Slack will prompt you to install the app to your workspace. Accept that and you're set.