Public/PartnerActions/Get-Tenants.ps1

function Get-Tenants {
    Param(
        [Parameter()]
        [string]$TenantId,
        [Parameter()]
        [string]$DefaultDomainName,
        [Parameter()]
        [string]$SearchString
    )
    process {
        Connect-CustomerGraph -CustomerTenantId $PartnerTenantId
        try {
            $Customers = Get-MgContract -All -ErrorAction Stop

            if($SearchString) {
                $Customers = $Customers | Where-Object { $_.DisplayName -like "*$($SearchString)*" -or $_.DefaultDomainName -like "*$($SearchString)*" }
            } else {
                if($TenantId) {
                    $Customers = $Customers | Where-Object { $_.CustomerId -eq $TenantId }
                } elseif ($DefaultDomainName) {
                    $Customers = $Customers | Where-Object { $_.DefaultDomainName -like "*$($DefaultDomainName)*" }
                }
            }
            $Customers
        }
        catch {
            throw "Failed to retreive customers from MS Graph: $_"
        }
    }
}