To add a check-in channel to a Post Check message campaign,
- Navigate to Guests > Segments > New Segment.
- Fill the Name and description (if any).
- Select the Segment type as "Guest Checkin".
- Under the Effective locations field, choose any "Location" or "Location group". You can also leave it blank if you wish to include all the locations.
- Under the Segment attributes, select Attribute - Event channel, Operator - Equal to, Value - Online order (or which channel you prefer).
- Select the Time duration and timezone.
- Click on Save.
- Then attach this segment to Post Checkin message campaign.