There are many reasons why a message might fail to send. Please check the error list below to see which one applies to your situation.
Message Sending Error List (Error Message / Cause / Solution)
Error Message | Affected OTA | Main Cause | Solution |
400 validation error | Airbnb | The message was blocked due to Airbnb's content policy. | Remove phone numbers or external URLs from the message and resend |
Content failed security filters | Booking.com | Links are restricted due to Booking.com's security filter. | Remove the shortened URL, change it back to the regular URL, and resend. |
Security policy blocked the message | All OTA | URLs not registered in the AirHost whitelist | Register the relevant URL in the Security Center, or turn off whitelist verification. After making the changes, please execute "Retry".
Related help: [Security Center] Enabling Message Security (Whitelist) |
Too many requests | Booking.com | Restrictions applied due to too many messages sent in a short time | Wait and resend later |
Message too large | All OTA | The attachment size has exceeded the limit. | Reduce image size to under 3.5MB and resend |
Sent but not received. | All OTA | Blocked by recipient email provider (e.g. carrier email) | Ask guest to use another email (e.g. Gmail), then resend |
Auto-reply not sent (no error) | Airbnb | Reservation is in “Request to Book” status | Resend after booking is confirmed. |
The email address is displayed as "@no-email-supplied.co" | Agoda / Jalan / Ikyu | OTA does not provide guest’s real email address | Contact via OTA messaging system |
You cannot send this message at this time | Airbnb | URL or contact info restricted in message | Remove the URL and phone number that were pointed out, revise the wording, and resend. |
Message cannot be sent | Trip.com | Restricted keywords (e.g. “credit card”) | Remove restricted words and resend |
Message sending error | Rakuten Travel | Character limit exceeded (over 750 characters) | Shorten message to within 750 characters and resend |
URL is masked | Agoda | There are no spaces before or after the URL. | Please add spaces before and after the URL and resend. |
Message not sent (rates/inventory normal) | Ikkyu | Login ID/Password Expired | Re-enter login information in channel settings * At Ikkyu, price availability is synchronized via API, and messages are handled via login-based integration. |
Steps to Check Details
① Check Reservation Status
Confirm whether the status is Confirmed
Ensure it is not in Request to Book status
On Airbnb, messages sent before reservation confirmation (Inquiry / Request to Book) may be blocked if they contain content that directs guests outside of Airbnb.
Examples of restricted content:
External website URLs
Phrases such as “Please check our website”
Any content suggesting booking outside Airbnb
When sending messages via the Airbnb website or app, you may still be able to send them after a warning is displayed. However, messages sent via API (such as through AirHost) may result in an error (400) and fail to send.
Therefore, it is recommended not to include external links or website references in automated messages before reservation confirmation.
② Check Message Content
Please ensure the following are not included in the message:
Phone numbers
Google Drive links or custom website URLs
Shortened URLs (e.g., bit.ly)
These may be blocked depending on the OTA’s policies.
③ Check AirHost settings
■ Is “Send after paid” turned ON?
Messages will not be sent for unpaid reservations.
■ Security Center (Whitelist)
Go to: Admin Console > Account Settings > Security Center > Security Settings > Message Security
If whitelist validation is enabled, messages containing unregistered URLs will not be sent.
■ "Don't send to these OTAs"
Please check the auto message editing screen to ensure that the target OTA is not excluded.
④ Guest Email Environment
Carrier email addresses (e.g., docomo, ezweb)
Spam/junk mail filters
Incoming email rejection settings
Even if AirHost shows the message as “Sent,” the guest may not receive it due to their email settings.