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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:
example
Or for longer, use three backticks above and below the code snippet:
longer
example
here
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, 18.0.2): 20.0.0.1
Operating system and version (eg, Ubuntu 20.04): Ubuntu 18.04.5 LTS
Apache or nginx version (eg, Apache 2.4.25): nginx/1.14.0
PHP version (eg, 7.1): 7.2.24
The issue you are facing:
sync breaks when enabling any of the 2FA, MFA etc.
Is this the first time you’ve seen this error? (Y/N):Y
Steps to replicate it:
- Enable 2FA
- use activesync
The output of your Nextcloud log in Admin > Logging:
Error: Undefined offset: 3 at /usr/local/lib/owncloud/lib/private/legacy/OC_Helper.php#548
(But i get this even without the 2FA activated.)
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'datadirectory' => '/home/user-data/owncloud',
'instanceid' => '',
'forcessl' => true,
'overwritewebroot' => '/cloud',
'overwrite.cli.url' => '/cloud',
'user_backends' =>
array (
0 =>
array (
'class' => 'OC_User_IMAP',
'arguments' =>
array (
0 => '127.0.0.1',
1 => 143,
2 => NULL,
),
),
),
'memcache.local' => '\\OC\\Memcache\\APCu',
'mail_smtpmode' => 'sendmail',
'mail_smtpauthtype' => 'LOGIN',
'mail_from_address' => 'administrator',
'passwordsalt' => 'dfgdfgdfg',
'secret' => '/dfgdfgdf',
'trusted_domains' =>
array (
0 => ''
),
'dbtype' => 'sqlite3',
'version' => '20.0.1.1',
'installed' => true,
'logtimezone' => 'Europe/Stockholm',
'logdateformat' => 'Y-m-d H:i:s',
'mail_domain' => '',
'loglevel' => 2,
'maintenance' => false,
'twofactor_enforced' => 'false',
'twofactor_enforced_groups' =>
array (
),
'twofactor_enforced_excluded_groups' =>
array (
),
'updater.secret' => '',
'mail_sendmailmode' => 'smtp',
);
Z-push-top log : OK:AuthenticationRequiredException
