Dear @Britt-Mari ,
By definition One-time suppliers are supported in Financials operations only and not in Purchase module.
According to the documentation One-time suppliers are supplier IDs that can be used to keep a record of the different supplier addresses where there is no need to follow-up on the total purchases and other figures per name and address.
Supplier specific information like name, address, tax number, AP supplier contact information and electronic bank address can be entered when an invoice for a one-time supplier is created.
It is possible to enter and update one-time specific information with the following processes:
Manual Supplier Invoice
Outgoing Supplier Invoice
External Supplier Invoices (no update of existing one-time information)
Supplier Analysis / Ledger Items
Supplier Payment Proposal Details
It is not possible to do purchase using a supplier record which does not have info in Supplier screen/Purchase tab as those info are needed for the purchase order process.
Further,If you are planning to use this supplier for frequent purchase transactions, it might be hard for you to maintain the record as one-time supplier. The idea of one-time functionality is to provide a master supplier to record one time purchases (less frequent), because there is no point to create a complete supplier master record in your AP, if you are not dealing with the supplier again. You can create a single one-time supplier and keep addresses separately for one time purchases. Under single supplier, you can keep bank accounts of the different supplier. So, one-time supplier will act as a master (dummy) supplier.