Enable SP Site Collection feature in powershell for all sites

Hello I would like to run a script to enable a site collection feature on all sites within a web application. Here is my script:

Add-PSSnapin -name "Microsoft.SharePoint.PowerShell"

$SPWebApp = Get-SPWebApplication http://sharepointtest/

foreach ($SPSite in $SPWebApp.Sites)
{

Enable-SPFeature -Identity Reporting -url $SPSite
}

I think I am not passing the url correctly as it gives this error:

Anyone know what I am doing wrong! Not the best with powershell by all means!