Sql 2017 mdm and ax2012 compatibilty?
No idea.
But. I think your setup isn't right. You have to specify the sql server(instance) not the mdc webservice(webapplication) url. This is what Sohaib already mentioned.
here is a link which containes a lot of other related links
www.1clickfactory.com/.../how-to-install-and-configure-master-data-management-for-ax2012
regards Douglas