Im trying to install portal and the webadaptor on the same machine as our ArcGIS Server (10.3) The install of portal was fine and I can access the site with https://MachineName.domain,com:7443/arcgis/home. When I install the webadaptor I also get no errors but when I access the site without the port number specified (https://MachineName.domain,com/arcgis/home) I get the message:

We are using an IIS webserver with all the neccessary ports open, SSL enables and bound to port 80 and 443 with a self signed certificate.
I am not IT person so my familarity with this is kinda low. I've followed the esri documentation much as possible but cant seem to resovle this. So close yet so far! Any ideas to point me in the right direction?