When configuring an Office 365 Group endpoint, you must enter the Office 365 Group site URL. The URL to be used will be one of the following two formats:
NOTE: Exclude the "/Shared%20Documents/Forms/AllItems.aspx" part of the URL.
To quickly find the SharePoint site URL for all Office 365 groups for the tenant, execute the following remote PowerShell commands:
NOTE: The commands will need to be run as the global administrator of the target tenant.
$cred = Get-Credential
$session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $cred -Authentication Basic -AllowRedirection
Get-UnifiedGroup | fl Displayname,SharePointSiteUrl