A buyer reference is the identifier a payer puts on a bank-rail transfer so the recipient can match it to an obligation - the UPI transaction reference, the SEPA end-to-end ID, the remittance information on a wire. On manual rails it is the reconciliation key: without it, a received payment is money without a meaning.
Crypto settlement reproduces the same idea differently: the transaction ID plus the checkout's address derivation does the matching automatically, which is why crypto legs do not need buyers to type references at all.
Every bank-rail settlement on U.CASH produces the rail's native references in the order view, and crypto legs reconcile by transaction and address. One export covers both vocabularies.
Every term behind the rails, the assets, and the settlement.