First to explain the meaning of two types of suppliers that are prospective and spend authorized. Prospective means a supplier which is a future supplier. You cannot enter into business with a prospective supplier, that means you cannot create PO's and Invoices against a Prospective supplier.
You can enter into business relationship with Spend authorized suppliers, like purchase of goods and pay them for the goods and services procured.

This type of requirement can be fulfilled by -
B. External Supplier registration-Prospective > Initiative > Supplier Response > Qualification valuation
> Promoted as spend authorized

You register the prospective supplier first, send the initiative to the supplier that means the qualification areas, then the supplier responds to the questions, after the response the evaluation team will evaluate and finalize. Then we will promote the supplier as spend authorized.