Owncloud connection could not be establishedwhen using ipad

Please help us by providing the following info.

Steps to reproduce
1. Use lastest version app on iPad 9.3.5

Expected behaviour
working normally
Actual behaviour
Tell us what happens instead
Connection could not be established
Mobile client configuration
Client OS (iOS
Client version:
Server configuration
Operating system:
Web server: linux
PHP version:
ownCloud version (see ownCloud admin page): 8.1.9
Updated from an older ownCloud or fresh install:
ownCloud log (data/owncloud.log):

Special configurations (external storage, external authentication, reverse proxy, server-side-encryption):

Might be related to:

Can you check the value of the following in your config/config.php:

'installed' => 'true'

When I change this parameter on the server, I cannot connect from the app anymore....

This sentence makes no sense. You already can't connect from the app as you have written in your initial post. Please clarify or be a little bit more precise...

I m connected, and get a list of files ready do be syncronized. But when I touch the file in order to get it on myiPad I get the message cannot connect to the server. Problem is only on my ipad . on Windows and via web browser it works

Do you use wifi in your home network? Or a mobile connection? Can you access via webinterface (on your webbrowser) on your iPad?
Can you see anything in your logfiles, for example a permission denied?

Can you connect the client on your iPad to demo.owncloud.org (user/pw: test/test)?