Booker Atom: Multiple critical bugs prevent multi-host bookings from working

[mattlgroff]

UPDATE: This issue grew into multiple related issues.

1. Parameter name mismatch (usernameList[] vs usernames[])
2. Event type API returning wrong data (id: 0, slug: "dynamic")
3. Frontend forcing dynamic override even with valid event slugs
4. Availability API not being called due to enabled condition

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Issue Summary

Booker atom does not load availability for dynamic bookings (multi-host via username joined with +).
When username="userA+userB", the calendar renders but no days/times become selectable because the GET /v2/slots/available request is not sent at all. With a single username, the request is sent and times render.

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Steps to Reproduce

1. Render the Booker atom with a combined username and valid event slug:

   <Booker eventSlug="thirty-minutes-video" username="campos-...-umbrage-com+aivory.lagto-...-umbrage-com" />

2. Observe that the calendar shows but no dates are selectable.
3. Change to a single username:

   <Booker eventSlug="thirty-minutes-video" username="campos-...-umbrage-com" />

4. Dates and times are selectable.

Any other relevant information: Booker should behave the same for single and multi-host bookings; the missing availability call prevents the UI from populating time slots.

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Actual Results

• Dynamic (two people): Calendar renders, no availability loads.
  Calls observed:

  • GET /v2/provider/<clientId>
  • GET /v2/atoms/event-types/thirty-minutes-video/public?username=<combined>
  • GET /v2/timezones
  • GET /v2/atoms/verification/email/check?...
  • Missing: GET /v2/slots/available?...

• Single person: Calendar renders with availability.
  Calls observed:

  • GET /v2/provider/<clientId>

  • GET /v2/atoms/event-types/thirty-minutes-video/public?username=<single>

  • GET /v2/timezones

  • GET /v2/atoms/verification/email/check?...

  • Present:

    GET /v2/slots/available
      ?usernameList[]=campos-...-umbrage-com
      &eventTypeId=2972117
      &startTime=2025-09-01T04:00:00.000Z
      &endTime=2025-10-01T03:59:59.999Z
      &timeZone=America/New_York
      &eventTypeSlug=thirty-minutes-video
      &_silentCalendarFailures=false
    

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Expected Results

• For dynamic bookings, Booker should send:

  GET /v2/slots/available
    ?usernameList[]=userA
    &usernameList[]=userB
    &eventTypeId=<resolved>
    &startTime=...
    &endTime=...
    &timeZone=...
    &eventTypeSlug=<slug>
    &_silentCalendarFailures=false
  

  and render selectable dates/times.

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Technical details

• Browser: Brave 1.81.137 (Official Build) (64-bit) — Chromium 139.0.7258.158
• Node.js: v22.16.0
• Component: @calcom/atoms → Booker

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Evidence

• Reproduced by rendering Booker with a combined username vs a single username as shown in Steps to Reproduce.
• The only functional difference observed is the absence of the GET /v2/slots/available call in the dynamic (two-person) case.

[linear]

CAL-6367 Booker Atom: Availability API (/v2/slots/available) not called for dynamic (multi-host) bookings

[mattlgroff]

Not sure if helpful or not, but here's what Claude Opus 4.1 says about this bug and potential causes/fixes. Could be totally wrong!

Bug Analysis & Solution Options

Root Cause Identified

The bug occurs in /packages/platform/atoms/booker/BookerPlatformWrapper.tsx:308-313. The useAvailableSlots hook has an enabled condition that requires Boolean(event?.data?.id). For dynamic events (multi-host bookings
with "+" separator), the event might not have an ID since it's a dynamic event type created on-the-fly.

enabled:
  Boolean(teamId || username) &&
  Boolean(month) &&
  Boolean(timezone) &&
  !event?.isPending &&
  Boolean(event?.data?.id), // ← Problem: Dynamic events may not have an ID

Solution Options

Option 1: Modify the enabled condition for dynamic events (Recommended)

// In BookerPlatformWrapper.tsx line 308-313
enabled:
  Boolean(teamId || username) &&
  Boolean(month) &&
  Boolean(timezone) &&
  !event?.isPending &&
  (isDynamic || Boolean(event?.data?.id)), // Allow dynamic events without ID

Option 2: Use a fallback event ID for dynamic events

// In BookerPlatformWrapper.tsx line 295
eventTypeId: isDynamic ? 0 : (event?.data?.id ?? 0),
// Update enabled condition
enabled:
  Boolean(teamId || username) &&
  Boolean(month) &&
  Boolean(timezone) &&
  !event?.isPending &&
  (isDynamic || Boolean(event?.data?.id)),

Option 3: Ensure dynamic events always get an ID from the API

• Modify the backend /apps/api/v2/src/modules/atoms/event-types/public endpoint to return a synthetic ID for dynamic events
• This would be more invasive but ensures consistency

Option 4: Create a separate condition for dynamic events

const shouldFetchSlots = isDynamic
  ? Boolean(teamId || username) && Boolean(month) && Boolean(timezone) && !event?.isPending
  : Boolean(teamId || username) && Boolean(month) && Boolean(timezone) && !event?.isPending && Boolean(event?.data?.id);

// Use in useAvailableSlots
enabled: shouldFetchSlots,

Additional Considerations

1. EventTypeSlug handling: The code already handles this correctly with eventTypeSlug: isDynamic ? "dynamic" : eventSlug || ""
2. Username list parsing: The getUsernameList(username) function correctly parses the "+" separated usernames
3. Backend support: The backend /apps/api/v2/src/modules/slots/slots-2024-09-04/services/slots-input.service.ts:123 returns a dynamic event when no specific event type is found

Testing Recommendations

After implementing the fix:

1. Test with single username (should still work)
2. Test with multiple usernames joined by "+" (should now fetch availability)
3. Test with team events (ensure no regression)
4. Verify the usernameList[] parameters are correctly sent in the API call

[mattlgroff]

This actually seems related to another Issue I'm seeing where the Availability Checker fails on multiple-users because the eventType is "dynamic" it's never finding any slots. This is hard-coded in the BookingAtomWrapper. If it gets multiple usernames it changes the eventType to "dynamic" but never finds open slots, it just returns empty for all.

[mattlgroff]

Actually even if you patch this to send an eventTypeSlug it still doesn't seem to work because the eventTypeId from the /public API call comes back as 0.

---

There it is! The API is returning "id": 0 and "slug": "dynamic" when you request a specific event type ("thirty-minutes-video") with multi-host usernames!

The backend is treating any request with multiple usernames (joined with "+") as a dynamic event request, completely ignoring the actual event slug you provided. It returns a generic dynamic event object with:

• id: 0 (no real ID)
• slug: "dynamic" (overriding your "thirty-minutes-video")
• isDynamic: true

This explains why the availability request fails - it's using eventTypeId=0 which is not a valid event type.

The issue is in the backend API - when it sees multiple usernames in the username parameter for the /v2/atoms/event-types/{eventSlug}/public endpoint, it returns a dynamic event instead of the actual requested event
type.

This is a backend API bug where it should either:

1. Return the actual event type with its real ID when a valid eventSlug is provided, regardless of multi-host usernames
2. Or return an error saying multi-host bookings aren't supported for specific event types

The frontend code in BookerPlatformWrapper.tsx is actually working correctly - it's just receiving bad data from the API!

[mattlgroff]

In addition to the above.. is you do send multiple usernames with a real eventTypeID and slug you get back 0 users. But it appears to be because of the following:

GitHub Issue Comment for #23560

Root Cause Identified: Parameter Name Mismatch in Multi-Host Bookings

After extensive investigation, I've identified the exact cause of why multi-host bookings fail to show availability.

The Problem

The Booker atom uses the wrong parameter name when requesting availability for multiple users. This causes the backend to receive an empty username list, resulting in no available slots being returned.

Root Cause

Parameter name mismatch between frontend and backend:

• Frontend sends: usernameList[]
• Backend expects: usernames[]

The backend code at /apps/api/v2/src/modules/slots/slots-2024-09-04/services/slots-input.service.ts:66:

const usernameList = "usernames" in query ? query.usernames : [];

The frontend code at /packages/platform/atoms/hooks/useAvailableSlots.ts:

usernameList: getUsernameList(username), // Sends as 'usernameList' parameter

Proof of the Issue

❌ FAILS - Using 'usernameList[]' (what frontend currently sends)

curl 'https://api.cal.com/v2/slots/available?usernameList[]=matt-cmdorvh9b002jqc1ti2wvmggi-umbrage-com&usernameList[]=dev1-cmdorvh9b002jqc1ti2wvmggi-eliostalent-com&eventTypeId=2972117&startTime=2025-09-03T04:00:00.
000Z&endTime=2025-09-10T03:59:59.999Z&timeZone=America/New_York&duration=30&eventTypeSlug=thirty-minutes-video'

Returns: {"data":{"slots":{}},"status":"success"}

✅ WORKS - Using 'usernames[]' (what backend expects)

curl 'https://api.cal.com/v2/slots/available?usernames[]=matt-cmdorvh9b002jqc1ti2wvmggi-umbrage-com&usernames[]=dev1-cmdorvh9b002jqc1ti2wvmggi-eliostalent-com&eventTypeId=2972117&startTime=2025-09-03T04:00:00.
000Z&endTime=2025-09-10T03:59:59.999Z&timeZone=America/New_York&duration=30&eventTypeSlug=thirty-minutes-video'

Returns: {"data":{"slots":{"2025-09-03":[{"time":"2025-09-03T17:30:00.000-04:00"}],"2025-09-04":[...]}}

Both users have availability individually, but when queried together with the wrong parameter name, the backend doesn't receive the usernames and returns empty slots.

Additional Issues Discovered

1. Event Type API Returns Wrong Data: When requesting /v2/atoms/event-types/{eventSlug}/public with multiple usernames (e.g., username=userA+userB), the API returns a generic dynamic event with id: 0 and slug: "dynamic"
   instead of the actual requested event type.
2. Frontend Overrides Event Slug: In BookerPlatformWrapper.tsx:315, the code forces eventTypeSlug: "dynamic" for multi-host bookings, even when a valid event slug is provided:
   eventTypeSlug: isDynamic ? "dynamic" : eventSlug || "",

Proposed Fix

Option 1 (Frontend fix - Simplest): Change the parameter name in /packages/platform/atoms/hooks/useAvailableSlots.ts from usernameList to usernames.

Option 2 (Backend fix): Update /apps/api/v2/src/modules/slots/slots-2024-09-04/services/slots-input.service.ts to accept both usernames and usernameList for backward compatibility.

Option 3 (Complete fix):

1. Fix the parameter name mismatch
2. Fix the event type API to return correct data for multi-host requests
3. Remove the forced "dynamic" override in BookerPlatformWrapper

Impact

This bug completely breaks multi-host/collective bookings in the Booker atom, as no availability is shown even when all participants have free slots. Fixing the parameter name should immediately resolve the issue.