Hi Renatas,
Try tx FTR_BAPI to ID the BAPI to use in your migration. Another option is create a Batch Input.
I had a migration (120) operations and they did them manually. I had 2 limitations:
1- Cashflow was in Excel
2- The Conditions of the Financial Transaction were not always clear (Interes Method, Amortization, Clasification, Tax Interest, etc) and have to checked manually
3- Different Product Types (Money Market, Values)
Kind Regards