The SAP system allows you to post invoices that do not refer to a PO or to a delivery. In contrast to invoices with a reference, the system does not propose any default values for the invoice items because it cannot determine any PO items or posted goods receipts (GRs) for this invoice.
In the Create Supplier Invoice – Advanced app and the MIRO transaction you have the following options for entering items without purchase order reference:
Posting to a general ledger (G/L) account
Posting to a material stock account
Posting to an asset
In the app Create Supplier Invoice you can additionally only post directly to G/L accounts.

If you create an invoice without reference, you must first enter the header data in the same way as for an invoice with reference. In the basic data, you enter invoice date, reference, invoice amount, and currency. However, you must also manually enter the invoicing party (in MIRO on the Details tab page). Only then you can enter items for G/L account, material, or asset.
Hint
For invoices without a purchase order reference, the payment terms are determined from the company code data of the supplier master record.
In the Create Supplier Invoice – Advanced app, unlike in the Create Supplier Invoice app, the terms of payment are determined only after you have entered an item.
For the Create Supplier Invoice – Advanced app and the MIRO transaction, you must activate direct posting to G/L account, material, and asset in Customizing. To do so, in Customizing for Materials Management choose Invoice Verification → Incoming Invoice → Activate Direct Posting to G/L & Material Accounts & Assets
Direct Posting to a G/L Account

You post to G/L accounts if, for example, amounts are settled for freight costs but you do not want to add these to the material or cost accounts for the invoice items.
In the Create Supplier Invoice – Advanced app or the corresponding transaction, on the G/L Account tab page, you can select different display variants to obtain the relevant account assignment fields in the item list.
Note
When posting directly to a G/L account, no posting is made to a GR/invoice receipt (IR) clearing account. The system posts manually entered G/L account lines directly to the G/L account specified. The control specified in the master record of the G/L account is taken into account. The system checks whether manual postings can be made to the account or whether it is subject to account assignment requirement.
Direct Posting to a Material

You post directly to material accounts (stock accounts), for example, if you want to post a subsequent credit or debit to a material, without an existing PO reference.
When posting directly to a material, no posting is made to a GR/IR clearing account. The system posts manually entered material lines directly to the stock account or price difference account, depending on price control and stock coverage. You must specify the plant as well as the material number and amount in order for the system to determine the material valuation and stock quantity. The system determines the existing stock quantities automatically. However, this proposed quantity can be overwritten.