When running the InstallPowershellExtensions task in Master_SingleServer.json, I got the following error:
HTTP Error 404. The requested resource is not found.
Upon further inspection, I noticed that it was making an HTTP request by default and not HTTPS, and the Sitecore site only had an HTTPS binding by default if you follow the standard installation.
From Master_SingleServer.json, I could see that the task was using a variable called UtilitiesBaseUrl:
Which had an http prefix:
Updated the UtilitiesBaseUrl variable to use https instead.