Personally Identifiable Information (PII)
An Onyx Mesh ledger is append-only. That is what makes it verifiable: nothing committed to it is edited, reordered, or removed, so a record read today is the record that was written. It also means anything written to it is permanent.
A ledger is therefore not an appropriate place to store personally identifiable information (PII) — names, email addresses, national identity numbers, dates of birth, card details, or anything else that identifies an individual and may one day have to be erased.
Keep that data in your own systems, where you can already answer for it, and put only a reference to it on the ledger. Account ids and tags are the natural place for an internal identifier or a hash; both are enough to correlate a ledger account with a customer record, and neither discloses who the customer is to anyone reading the ledger.