VirtualCollab

Goood day I am trying to check if the client has selected the bank transfer so that on the invoice it will populate with banking details but i get the error below BANK TRANSFER PAYMENTS if ($paymentmethod=="Bank Transfer") { $pdf->SetXY(15, 88); $pdf->SetFont('$pdfFont','B',10); $pdf->Cell(180,15,"Payment Due Via Bank Transfer",0,0,'R'); $pdf->Ln(10); $pdf->SetFont('$pdfFont','',9); $pdf->Cell(0, 4, "Bank: Standard Bank", 0, 1, 'R'); $pdf->Cell(0, 4, "Name: MOLTEQ BUSINESS SOLUTIONS (PTY) LTD", 0, 1, 'R'); $pdf->Cell(0, 4, "Branch code: 6105", 0, 1, 'R'); $pdf->Cell(0, 4, "Account No: 10 15 336 681 6", 0, 1, 'R'); $pdf->Cell(0, 4, "SWIFT code: 123456789", 0, 1, 'R'); $pdf->Cell(0, 4, "Reference: #$invoicenum", 0, 1, 'R'); $pdf->Ln(10); } but i get this errror TypeError: Argument 1 passed to WHMCS\Order\Order::add() must be of the type int, null given, called in /home/ftsmnyjc/clients.virtualcollab.co.za/includes/orderfunctions.php on line 0 and defined in /home/ftsmnyjc/clients.virtualcollab.co.za/vendor/whmcs/whmcs-foundation/lib/Order/Order.php:0 Stack trace: 0 /home/ftsmnyjc/clients.virtualcollab.co.za/includes/orderfunctions.php(0): WHMCS\Order\Order::add(NULL, '8276580533', 'bank transfer', '', 0, 74, 0) 1 /home/ftsmnyjc/clients.virtualcollab.co.za/cart.php(0): calcCartTotals(NULL, true, false) 2