Haproxy + letsenrypt. hostname directs to another port

[sintei]

Sorry for the probably bad headline.

I have a container (small server) with MySQL installed. Reachable at 192.168.1.2:443
I have set it up so lets encrypt fetches a wildcard cert *.contoso.com, added the name mysql.contoso.com in frontend/backend as ACL (or whatever its called). And also in the DNS resolver.

It works, so when I go to mysql.contoso.com the page pops up.
However, on that page, there are 3 buttons (webmin, shell and adminer). They point to different ports: 12320, 12321 and 12322 withe the same IP of course.

if I go to the page by IP, I can see the page, click the button and it will take me to that service corresponding to the port.
But when I use the hostname, I see the page, click the button, and then it just times out.

I take it I have to add these ports somewhere in either front or backend?

Help appreciated!