418 Error While Syncronising Contacts

Nextcloud version : 26.0.1
Operating system and version : Linux 5.4.32-grsec-grsec-plus+ x86_64
Apache or nginx version (eg, Apache 2.4.25): Apache 8.1.17
PHP version: 8.1

The issue you are facing:
I’m experiencing two different problem with NextCloud Contacts. Not sure if they’re related or not.

First problem is that new contacts aren’t being saved. If I export them from my phone into a .vcf file, then import them into nextcloud through the web interface, everything imports as expected, except for 5 contacts that cause an error. However, if i create a new contact, or edit an existing contact directly in NextCloud, the information is not saved, or only part of it is saved. For example, it might save the first 3 characters of the new contact’s name, but not the phone number or address. I am hitting the enter button, and focusing the cursor onto an new field after editing each field.

The second problem is I’m attempting to use DAV5x to synchronise contacts and calendars with my phone. Calendars synchronise perfectly, and all contacts that are created or imported directly into NextCloud through the web interface will synchronise with the phone (android). However, as soon as I create a new contact, or edit an existing contact in the phone, the syncronisation fails, and throws an HTTP 418 error.

This is a clean installation of NextCloud. I never had any problems with creating or synchronising contacts on the previous installation.

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:

1. Install Own Cloud, and contacts on server.
2. Install DAV5x on Android.
3. Attempt to create or synchronise contacts.

The output of your Nextcloud log in Admin > Logging:

No log file created for error.

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

$CONFIG = array (
  'instanceid' => '',
  'passwordsalt' => '',
  'secret' => '',
  'trusted_domains' => 
  array (
    0 => 'my.url.com', 'www.my.url.com',
  'datadirectory' => '/home/user/my.url.com/data',
  'dbtype' => 'mysql',
  'version' => '',
  'overwrite.cli.url' => 'my.url.com',
  'dbname' => 'dbname',
  'dbhost' => 'mysql.my.url.com',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'dbuser',
  'dbpassword' => 'password',
  'installed' => true,
  'app_install_overwrite' => 
  array (
    0 => 'duplicatefinder',

Nobody has encountered a 418 error on a fresh installation?