It is possible to import data without a unique ID (e.g. customer number). However, we recommend that all data records - both customers and leads - have a unique ID. Without a unique ID, problems may arise during subsequent data updates, as the data records cannot be reliably and unambiguously assigned (see Update customers).
To ensure a smooth import and problem-free data updating, we recommend assigning a unique ID for all data records in advance (see Key fields (IDs)).