What causes the Approved_Amount field in the AP Invoices table to populate?

Oracle R12 SQL query:

SELECT *

FROM  AP.ap_invoices_all

WHERE invoice_date >= '01-JAN-20'

AND  approved_amount IS NOT NULL

GROUP BY SOURCE

UNION ALL 

SELECT source, count(1)

FROM  AP.ap_invoices_all

WHERE invoice_date >= '01-JAN-20'

AND  approved_amount IS NULL

GROUP BY SOURCE

Provides:

Where the Approved_Amount field is populated with a value for a given invoice. What is the difference between the two Manual Invoice Entry lines (as only one is in the Payables Sources lookup)?

Thank you in advance,

Lonnie