Problem with MS Excel MDS addon - unable to connect to the web app

I have a new installation of MDS and SQL Server 2016. Installed the Excel plugin too, but unable to connect to the web app. I keep getting this error "there was no endpoint listening at > that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details (mscorlib)" The URL is correct, I don't have extra items in the URL (like default.aspx etc). It isn't https, just http. The same URL works in the browser. What else can I check?