Try below PowerShell command for the relative path for the URL:
$web.SelfServiceCreationParetntSiteUrl = "/relativePath/[%userid%]" $web.update();
The output will be like below:
You can visit this link for more information on set up User Profile My site using PowerShell.
Above code sets link for "Prompt user to create team site under". But its not selected by default.Need to write code as below for link to be set and selected.
$web.ShowStartASiteMenuItem=$True $web.Update() $web.SelfServiceCreateIndividualSite=$True $web.SelfServiceCreationParetntSiteUrl = "/relativePath" $web.update()
Above code sets the link and also make it selected for "Prompt user to create team site under".