Support intro
Sorry to hear you’re facing problems 
help.nextcloud.com is for home/non-enterprise users. If you’re running a business, paid support can be accessed via portal.nextcloud.com where we can ensure your business keeps running smoothly.
In order to help you as quickly as possible, before clicking Create Topic please provide as much of the below as you can. Feel free to use a pastebin service for logs, otherwise either indent short log examples with four spaces:
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Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 20.0.5): 27.0.2
Operating system and version (eg, Ubuntu 20.04): Ubuntu 22.04
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.52
PHP version (eg, 7.4): 8.1
The issue you are facing:
At least one user I have cannot be invited to any calendar event on the Nextcloud.
Is this the first time you’ve seen this error? (Y/N): Y, but I’ve never tested this particular user before.
Steps to replicate it:
- Create an event on the calendar
- Go to add this one user (all other tested are fine).
- The sidebar window just shows a spinning icon and never resolves.