Issue: The .APPLICATION file can not be downloaded – VisualSP Online site collection installer
Edge Extension\Safari Extension
Cause: Windows bug exposed when you are using a proxy server and you bypass the proxy for local addresses
Solution: Install the HotFix and/or apply the workaround presented by Microsoft here: https://support.microsoft.com/en-us/help/952324/fix-you-cannot-download-the–application-file-when-you-deploy-an-appli
Diagnostic steps: When you click the link to download VisualSPOnlineHelpApp.SiteCollectionConfigWizard.application , the file doesn’t download, but you are presented with a screen showing an OneClick installation error log. The log information matches that at the above Solution link.