As employee to be able to book time off directly from Slack, you will have to follow the following steps:
After you can use /lb in any channel.
Note: If you get an error, mentioning "Your account is not associated with any company", please ask your administrator to invite to the LeaveBoard system. Administrators can do this by following these instructions. https://leaveboard.com/support/setup-import-slack/
Note: If they have invited you to use LeaveBoard using your company email, however on Slack you use a different email, you will not be able to use the /lb command.