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Sorry to hear you’re facing problems 
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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, 12.0.2):18.03
Operating system and version (eg, Ubuntu 17.04):Ubuntu Server 18.04.4 LTS
Apache or nginx version (eg, Apache 2.4.25): Apache 2
PHP version (eg, 7.1):PHP7.2
The issue you are facing:
After the nextcloud is set up, it can be used normally;and then the nextcloud cannot be used after the onlyoffice-documentserver is set up,Internal Server Error, nothing in logs.
Is this the first time you’ve seen this error? (Y/N):Y
Steps to replicate it:
The output of your Nextcloud log in Admin > Logging:
PASTE HERE
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => 'ocx83huzhotc',
'passwordsalt' => 'KYRY3YPLmIGlgtEVOMQzGPye/B2nPq',
'secret' => 'uK9ZiSyuMSS+7Tofhvg9ztIbAPCOgr0B/xkye+3gDRojO4V5',
'trusted_domains' =>
array (
0 => 'XXX.XXX',
),
'datadirectory' => '/data',
'dbtype' => 'mysql',
'version' => '18.0.3.0',
'overwrite.cli.url' => 'https://XXX.XXX',
'dbname' => 'nextcloud',
'dbhost' => 'localhost',
'dbport' => '',
'dbtableprefix' => 'oc_',
'dbuser' => 'XXXX',
'dbpassword' => 'XXXXXX',
'installed' => true,
'loglevel' => 0,
);
The output of your Apache/nginx/system log in /var/log/____:
[Wed Apr 01 12:04:12.475567 2020] [mpm_prefork:notice] [pid 1656] AH00163: Apache/2.4.29 (Ubuntu) OpenSSL/1.1.1 configured -- resuming normal operations
[Wed Apr 01 12:04:12.789667 2020] [core:notice] [pid 1656] AH00094: Command line: '/usr/sbin/apache2'
www.XXX.XXX 192.168.10.1 - - [01/Apr/2020:12:23:18 +0800] "GET /status.php HTTP/1.1" 400 3757 "-" "Mozilla/5.0 (Windows) mirall/2.6.4stable-Win64 (build 20200303) (Nextcloud)"