invoice approvals required for only iSupplier invoices

hi,

We are on R12.2

Currently we do not have any invoice approvals in place.

All invoices are keyed in manually.

Now, we are going live with iSupplier portal.

We want only invoices originating from iSupplier portal to be sent to approval. ( invoice approval workflow )

All other invoices should not require any approval.

How can this be achieved ?

Thx,

Daniela