Ensure you meet the following requirements prior to installing Web Designer and Web:
•You need an ArcGIS Online or Portal for ArcGIS identity to sign in to Web Designer and Web.
•If you plan to host on a website in IIS that is not the Default Web Site, you should have, or create that website before you run the Post Installer.
•You must create an app for Web in your organization's Esri portal, as you need it to obtain an App ID and a Redirect URL used during the installation process. The application must be registered. In some organizations, this can only be done by Administrators.
For the on-premises version of Web, an Organizational or Developer account is necessary for ArcGIS Online. To create an App for Web in your organization's Esri portal, you need at least a Creator user (formerly, a Level 2 user) or a GIS Professional user.