Can not reach Seafile with Apache on Openmediavault

Hello experts,
I tried to install the latest Seafile Server 7.0.5 on my Openmediavault 5 NAS based on Debian 10.
Unfortunately I can’t reach the Web interface.

My ccnet.conf:

[General]
 USER_NAME = NAS
 ID = 9b4260af2b7313e64c722d8fdf6043b8ca3fb95b
 NAME = NAS
 SERVICE_URL = http://192.168.178.60:8000
 
 [Client]
 PORT = 13419
 
 [Database]
 ENGINE = mysql
 HOST = 127.0.0.1
 PORT = 3306
 USER = *****
 PASSWD = *****
 DB = ccnet-db
 CONNECTION_CHARSET = utf8

Apache ports.conf

Listen 8999

<IfModule ssl_module
Listen 883
</IfModule

<IfModule mod_gnutls.c
Listen 883
</IfModule

000-default.conf

<VirtualHost *:8999
DocumentRoot /var/www

 Alias /media  /opt/seafile/seafile-server-7.0.5/seahub/media
RewriteEngine On

 <Location /media
     Require all granted
 </Location

 #
 # seafile fileserver
 #

 ProxyPass /seafhttp http://127.0.0.1:8082
 ProxyPassReverse /seafhttp http://127.0.0.1:8082
 RewriteRule ^/seafhttp - [QSA,L]
 #
 # seahub
 #

 SetEnvIf Authorization "(.*)" HTTP_AUTHORIZATION=$1
 ProxyPreserveHost On
 ProxyPass / http://127.0.0.1:8000/seafile
 ProxyPassReverse / http://127.0.0.1:8000/

</VirtualHost

I am using Port 8000 because 80 is reserved by the OMV Webinterface.

Any hints are appreciated.

Best regards,
Heinrich