Failed to use W10 nexcloud client through ssl

Nextcloud version : 14.0.3
Operating system and version : freenas/freebsd 11.2
Apache or nginx version : ?
PHP version : ?

First of all my issue is not coming from owncloud directly whose is running like a charm. Here is my trouble :

I installed a reverse proxy based on Pound in a freebsd jail with ssl listening service, even if i’m able to safely browse nexcloud web interface now, nexcloud W10 client is failing to connect to the server (and android app too). I probably forgot something within the Pound script, could you please help me ?

Thanks a lot in advance