Collabora server IP address could not be found

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Nextcloud version : 19.0.0
Operating system and version : Ubuntu 18.04.4 LTS
Apache : 2.4.29
PHP version : 7.2.24

Issue:
I’ve got Nextcloud installed and am wanted to install Collabora Online, I followed the tutorial at here: https://www.linuxbabe.com/cloud-storage/integrate-collabora-online-server-nextcloud-ubuntu

Everything seemed to work fine, however, when I try to open a document in nextcloud it shows “collabora.mydomain.com’s IP address could not be found”.

Nextcloud was installed and accessible by my domain “office.mydomain.com”, after following the guide above it no longer is, but is accessible by “office.mydomain.com/nextcloud”.

Edit: I re-wrote the nextcloud.conf to route to the subdomain again, I can access nextcloud from the correct address again, still can’t open documents though

I presume the issue is something to do with the DNS/ Proxy stuff, to be honest I’m very new to all this to have no idea what I’m talking about but am trying my best lol

Any help would be graciously received!