Functions/Get-GSuiteGroupMember.ps1

<#
.SYNOPSIS
    This function gets the members of a GSuite group.
    This function returns either PSCustomObject when there is one member, or Object[] when there is more than one member.
#>

function Get-GSuiteGroupMember {
    [CmdletBinding(PositionalBinding=$false)]
    [OutputType([Object[]], [PSCustomObject])]
    param (
        # The primary email address of the group.
        [Parameter(Mandatory=$true)]
        [ValidateNotNullOrEmpty()]
        [String]$primaryEmailAddress
    )

    # Validate that the 'connection' has been established and the group access token exists
    Assert-GSuiteConnection -Scope "Group"

    # Prepare REST call parameters
    $invokeRestMethodParams = @{
        Uri     = "https://www.googleapis.com/admin/directory/v1/groups/$($primaryEmailAddress)/members"
        Method  = "GET"
        Headers = @{
            Accept        = "application/json"
            Authorization = "Bearer $($Global:GSuiteAccessTokensHashTable.Group)"
        }
    }

    # Invoke the REST call
    $response = Invoke-RestMethod @invokeRestMethodParams
    return $response.members
}