Let's Encrypt on 2 domains

My YunoHost configuration

Hardware: x64 computer
Internet access: ethernet at home
YunoHost version:
yunohost: 2.7.10
yunohost-admin: 2.7.7
moulinette: 2.7.7
ssowat: 2.7.7
Have you personalized your yunohost with some specifics configurations or do you use only the yunohost cli/webadmin tool ? basic

Description of my problem

I have 2 domains, and I have tried searching around for a tutorial as to how it works. I have noted what guide I found to be most relevant.
I have had domain1 in use for some time, and that and sub-domains run like a charm. I bought another domain, domain2. Everytime I try to access it, with, let’s say mattermost installation, it re-directs to domain1 and I get creepy blocking in Firefox.

Note. Both domains have Let’s Encrypt certificates installed from the web admin site.
What I have read to try and understand it: https://yunohost.org/#/certmanager

I thank you in advance.