I'm trying to set-up a multi site. It's not working and I can't see what I've done wrong

Main site is 'nordikota', and OC is installed in the default directory.
Trying to set-up another called 'teesquad'
Created a sub-domain called teesquad.nordikota.co.uk. Document root is '/public_html'
In Admin, created a new default user for the new site
Under settings, added a new site called TeeSquad and used the URLs of https://teesquad.nordikota.co.uk
Filled all the rest of the info in.
When I go to teesquad.nordikota.co.uk, I get the main site and it shows nordikota.co.uk in the address bar. There are no re-directs in place.
I can't get past this bit & can't see what I've set-up wrong.
Any ideas?