What causes "Failed to add guests to the booking" in calcom/cal.diy?

Check server logs — addGuestsHandler may log the specific reason it didn't return 'Guests added'.

calcom/cal.diy · error · HttpException

Failed to add guests to the booking

Error message

Failed to add guests to the booking

What it means

A 500 HttpException thrown by BookingGuestsService_2024_08_13.addGuests when the addGuestsHandler returns successfully but its response message is not the expected 'Guests added' string. This indicates the handler completed without throwing but didn't perform the expected operation — an unexpected internal state.

Source

Thrown at apps/api/v2/src/platform/bookings/2024-08-13/services/booking-guests.service.ts:55

      );
    }

    const platformClientParams = booking.eventTypeId
      ? await this.platformBookingsService.getOAuthClientParams(booking.eventTypeId)
      : undefined;

    const emailsEnabled = platformClientParams ? platformClientParams.arePlatformEmailsEnabled : true;

    const res = await addGuestsHandler({
      ctx: { user },
      input: { bookingId: booking.id, guests: input.guests },
      emailsEnabled,
      actionSource: "API_V2",
    });
    if (res.message === "Guests added") {
      return await this.bookingsService.getBooking(bookingUid, user);
    } else {
      throw new HttpException(
        "Failed to add guests to the booking",
        500
      );
    }
  }
}

View on GitHub (pinned to 176037d0af)

Solutions

Check server logs — addGuestsHandler may log the specific reason it didn't return 'Guests added'.
Verify the booking is in a state that supports guest addition (ACCEPTED or PENDING, not CANCELLED).
Check if any of the guest emails are already registered as attendees — duplicates may cause a non-success message.
If using platform OAuth client settings, verify arePlatformEmailsEnabled and related settings aren't causing a silent rejection.
Report to Cal.com if the handler returns an unexpected message with no logged explanation — this may be a bug.

Defensive patterns

Strategy: try-catch

Try / catch

try {
  await api.addGuests(bookingUid, guests);
} catch (err) {
  if (err.statusCode === 500 && err.message === 'Failed to add guests to the booking') {
    // Unexpected internal state — check server logs and retry once
    console.error('Guest addition returned unexpected state for booking', bookingUid);
    await api.addGuests(bookingUid, guests); // single retry
  } else { throw err; }
}

Prevention

Verify the booking is in an active state (ACCEPTED/PENDING) before adding guests.
Check for duplicate guest emails — duplicates may cause a non-success handler response.
If using OAuth client settings, verify arePlatformEmailsEnabled is configured correctly.
Log the full request payload when this error occurs to help diagnose the handler's unexpected response.

When it happens

Trigger: POST /v2/bookings/{bookingUid}/guests where addGuestsHandler (from @calcom/platform-libraries/bookings) resolves without throwing but returns a response object whose .message field is something other than 'Guests added'. This could be a partial success, a silent failure, or a version mismatch in the handler's response contract.

Common situations: The addGuestsHandler internally encounters an issue (e.g., email delivery disabled, attendee already exists) and returns a different message instead of throwing. A library version mismatch where the handler's response message format changed. An edge case in the handler logic where the booking is in a transitional state.

Related errors

AI-assisted analysis of calcom/cal.diy@176037d0af (2026-08-12). Data as JSON: /api/errors/06e7b3cc7ca282db. Report an issue: GitHub.