Booking an appointment in a free slot returns "The appointment could not be booked. No available users found. Can you try another time slot?"

[G00mbah]

Issue Summary

I tried to plan an appointment for a customer in a free slot. So the slot was selectable and after filling in all the necessary fields it returns (translated from Dutch): "The appointment could not be booked. No available users found. Can you try another time slot?"

Steps to Reproduce

1. Click on an empty slot
2. Book an appointment
3. Get the error

Actual Results

The appointment can't be booked although it is being booked in a free slot, which is also free in the actual Proton calendar.

Expected Results

I expect the appointment to be booked.

Technical details

• Chrome Version 139.0.7258.139 (Official build) (64-bits) with Proton calendar

Evidence

Screens:

September 11th 13.00 is available in calendar:

Slot can be booked on Cal:

Availability shows it as blocked:

[linear[bot]]

CAL-6332 Booking an appointment in a free slot returns "The appointment could not be booked. No available users found. Can you try another time slot?"

[CarinaWolli]

@G00mbah do you have any way how we can reproduce this? This this happen once or does it keep happening?

[zhyd1997]

The error is thrown here by creating a booking here: https://github.com/calcom/cal.com/blob/bfa23ddb8085801cac0649cd8bce8dcbb88c8ebb/apps/api/v2/src/ee/bookings/2024-08-13/services/bookings.service.ts#L154

https://github.com/calcom/cal.com/blob/bfa23ddb8085801cac0649cd8bce8dcbb88c8ebb/apps/api/v2/src/ee/bookings/2024-08-13/services/errors.service.ts#L34-L41

[jadhavharshh]

Can you provide more details on how we could recreate this error?

[G00mbah]

@G00mbah do you have any way how we can reproduce this? This this happen once or does it keep happening?

@CarinaWolli

This unfortunelatley keeps happening. I could provide the Proton feed URL for reproduction but would prefer to send that privately. How can I get that URL to you?

[CarinaWolli]

@G00mbah I forwarded this to the team to have a look at it. I will get back to you

[zhyd1997]

Similar issue: https://github.com/calcom/cal.com/issues/20406

[jmicrobe]

Hello, I'm having the same problem. Also using proton calendar with an ICS feed, and gcal with an ICS feed.

I think I've identified the issue in my case. I'm using proton but also want cal.com to check a google calendar for conflicts. It's the google calendar that's causing issues. I want to use the ICS feed for the google calendar, because when I add the gcal app to cal.com it automatically defaults to adding events to the gcal, and removes the option to add events to my proton calendar (via ICS feed). I do not want events added to the gcal, I want them added to proton.

I've tried all of the URLs from gcal to link to cal.com via ICS and every one that I'm able to enter (that correct updates my availability) will spit out the "no available user found" error. When I remove the gcal, I have no issues and am able to add events to my proton calendar.

[ldealmei]

Hi all, This issue seems has been running for some time now with no clear signs that it'll be fixed soon.

Since it is really blocking for me, I've found a workaround. You will need a gmail account for this to work. The workaround is to sync your freebusy Proton Calendars with Google Agenda and do the cal.com booking via Google Agenda.

It goes as follows:

1. Get free/busy public links from your ProtonMail calendars (paste them somewhere in a notes app)
2. Follow the instructions in this repo: https://github.com/derekantrican/GAS-ICS-Sync?tab=readme-ov-file
3. Do a startSync run, to sync a first time and check that it is working properly. Then do an install run.
4. In cal.com, remove your Proton ICS feeds and instead install the Google Calendar app
5. Test booking a slot

Normally it should work fine.

The downside is that you need to manually input the booked events in your Proton Calendar but if you don't have 100s it's not really an issue as you get an email with the ICS.

Hope this helps

[monty241]

Still reproduces on v.5.9.0-h-9e10dfd

Console:

Error ----> end of line ---> c.js?i=5&v=3&h=cal.com&r=1:1 

POSTto https://cal.com/api/book/event raises 409

Payload sent:

{
  "responses": {
    "name": "John Doe",
    "email": "[email protected]",
    "location": {
      "value": "integrations:daily",
      "optionValue": ""
    },
    "guests": [],
    "smsReminderNumber": "+31621228293"
  },
  "user": "some.one",
  "start": "2025-11-19T13:30:00+01:00",
  "end": "2025-11-19T14:30:00+01:00",
  "eventTypeId": 1986106,
  "eventTypeSlug": "onboarding60",
  "timeZone": "Europe/Amsterdam",
  "language": "nl",
  "metadata": {},
  "hasHashedBookingLink": false,
  "routedTeamMemberIds": null,
  "skipContactOwner": false,
  "_isDryRun": false,
  "dub_id": null
}

Response:

{"message":"no_available_users_found_error","data":null}

[adityaathalye]

This bug is vexing me :(

Below is a live event on my actual live calendar that you can use to reliably reproduce the bug. I cloned an actual event I want to use, but can't, because of this annoying bug.

As of this comment's submit time, the bug triggers this way:

• GOTO: https://cal.com/evalapply/github.com-calcom-cal.com-issues-23391
• Try booking a 90 minute slot at 8:15am. - This will FAIL with the "no available user" error.
• Then, try booking a 90 minute slot at 10:00am - This will work. (not 8am, not 9am, but 10am, for this calendar)

What I think is going on:

• I want people to be able to book a time slot starting any 15th minute of the day.
• However cal.com's logic uses the user-selected "Available Duration"---in this case, 90 minutes---to divide the day into equal, back-to-back, intervals.
• And then, it accepts a booking ONLY IF the user-selected start time coincides with the start time of one of cal.com's intervals.

This is obviously wrong. Intervals should be calculated based on the time increments offered by me, the scheduler. In this case, a person should be able to book a 90 min slot, starting at 8 am or 8:15 am or 8:30 am.

nb. I will keep this event type alive as long as I don't get spammed on it :)

[adityaathalye]

Hi @CarinaWolli and @emrysal , is a fix upcoming anytime soon?

Just some rough idea will be great (Q1'2026? Q2'26? ...), so one can work around this issue until then.

Issue #20406 also reports the same problem. As you can see from the discussion there, it's a really bad look for us with our prospects and customers, if they see open slots and keep getting the "no available users" error. I've had a couple of embarrassing situations already in the last few weeks, since I started using cal.com (SaaS service).

nb. Just surfacing real-world impact, so cal.com team can better assess relative importance.

I understand competing product priorities... I see the 0.6.0 release appears to have been a big one. Congrats on shipping!

[emrysal]

Hi @adityaathalye - aiming to have a diagnosis for this issue and a fix on the way by end of week 👍

[adityaathalye]

@emrysal Cool! I hope the live calendar in my earlier comment helps debug this.