Short answer
Lending-to-core integration should begin by defining system-of-record and ownership for customer, account, transaction, balance and accounting events before choosing APIs, events, batch or files.
Why this matters
This design choice directly affects correctness, control, integration and auditability.
Questions to answer before design
What is the system of record? Where do rules live? Which data is sensitive? What evidence must be retained? Who owns operations after go-live?
Frequently asked question
Is there one correct design for every organization?
No. Final design depends on products, policy, existing systems, data, risk and the institution’s operating model.