Public/Marketing/Companies/New-CWMMarketingGroupCompany.ps1

function New-CWMMarketingGroupCompany {
    # 2021.1
    [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSShouldProcess', '', Justification = 'Used by sub-function')]
    [CmdletBinding(SupportsShouldProcess, ConfirmImpact='Medium')]
    param(
            [Alias('parentId')]
            [int]$groupId,
            [Alias('companyId')]
            [int]$id,
            [boolean]$defaultContactFlag,
            [boolean]$allContactsFlag,
            [boolean]$unsubscribeFlag
    )

    $Endpoint = "/marketing/groups/$($groupId)/companies"
    Invoke-CWMNewMaster -Arguments $PsBoundParameters -Endpoint $Endpoint
}