Add User ID To Invoice Template

I have the correct code snippet for customizing the invoice template, but am unsure on how to implement this specific item (user id).

Here is the code with other customization snippets, in red, in site.php:

Code:

Am_Di::getInstance()->hook->add(Am_Event::PDF_INVOICE_COL_RIGHT, function (Am_Event $e) {
    $payment = $e->getPayment();
    $inv = $payment->getInvoice();
    $col = $e->getCol();

    //$col->add("PO# {$inv->purchase_order}");
    //$col->moveBefore('date', 'invoiceNumber');
    //$col->prepend('Reçu de transaction'); //prepend line
    //print_rre($user);

    $col->remove('name');
    $col->remove('email');
    $col->remove('address');
    $col->remove('city');
    $col->remove('country');

    $col->add('Date: ' . amDate($payment->dattm), 'date');  <<<<<THIS ONE
    $col->add('Invoice Number: ' . $payment->invoice_id, 'invoiceNumber'); <<<<<AND THIS ONE
   
    if($inv->paysys_id == "offline"){
        $col->add('Payment Method: PURCHASE ORDER');
    } elseif($inv->paysys_id == "authorize-cim"){
        $col->add('Payment Method: CREDIT CARD');
    } else {
        $col->add('Payment Method: ' . strtoupper($inv->paysys_id));
    }


    if($inv->paysys_id == "offline"){
        $col->add("P.O. Number: {$inv->purchase_order}");
    }

});

I would like to add the user id to the right column, below the PO# as shown in the attached image:

https://imgur.com/a/UCZpEpw



If anyone could help with the right line of php, I would be grateful.

Thanks,

Roger

Thanks Caesar!