Go to A/P>>PO Reconciliation

 Use the filters to find the PO that the invoice will be uploaded for. Then go to the Vendor's Invoice column for a given PO and click on Upload.

The Upload Invoice window will pop up. Enter the invoice number and the total amount of the invoice in the corresponding fields. If you have the invoice in a PDF file, drag the file towards the dotted area and drop it on the "Drag your file here or click to upload" section. Once you click on Save, the invoice will be listed below in the Invoice Summary with the uploaded invoice associated with it.

Notice that you can also associate additional Charges per invoice by clicking on the link next to the Total Invoice field. Keep in mind that the total of additional charges should not exceed the total of the invoice. Just enter the amount and hit the Enter key. Once you have finished, click on Close. The additional charges with the same description will be consolidated in the PO Reconciliation screen as additional PO charges.

Make sure that the PO total corresponds to the total of the invoices associated with it. 

Click on Close to finish. The invoices added will be listed on the Vendor's Invoice column and by hovering the cursor over that field the system will pop-up the invoice details and you will be able to perform some actions, for example, if you click on View, the system will download the invoice.