There seems to be a bug with shortcode of [house rules] in my case.
This [house rules] is called in the scheduled message, causing the message is not being sent.
I have talked to Airbnb support and they are aware about this bug and is escalated to the technical team.
I have been host for many years and this error happens only after Airbnb introduce new feature with more granular settings, sometime in early January 2024.
While waiting I try the workaround as follows:
1. Edit the template of the scheduled message that is in error
2. Remove the problematic [house rules] short code
3. Type the house rules manually in that schedule message
4. Save
Once I do that the error message on the guest reservation Inbox is gone. Yeayy... !
I hope this helps, while waiting for Airbnb technical team rectifying the issue.