How to put iSupplier invoices on Hold?

We are implementing iSupplier Portal and Supplier will be creating invoice against PO and adding shipment and Handling charges(Freight and Miscellaneous) to the invoice.

Requirement is to place all the iSupplier invoices on hold, to stop proceeding further with validation/accounting/payment. Business team wants to review each iSupplier invoices before payment.

We are using Vertex tax system for tax calculation, so supplier will not be adding tax lines to the invoice. So either AP team wants to add tax line manually or Vertex can add tax line to iSupplier invoices.

What is the best approach to place iSupplier invoices on hold as soon as it creates? Please help with steps.