To ensure that a field is populated on every single record, regardless of how it is created (manually, via API, or through an integration), the best method is to make the field universally required at the field definition level. When a field is marked as " Required " in the Object Manager, the Salesforce database will reject any attempt to save a record if that field is empty. While requiring a field on a Page Layout or Record Type (Option B) provides a good user experience for manual entry, it does not prevent records from being created without that data via the API or background processes25. Using a flow (Option A) to update the field is reactive rather than preventative26. Universal requirement is the most robust way to maintain data integrity for critical fields like " Billing System " that are essential for reporting and external system alignment.