qualifier number + unit a measured amount

tier flat fee

An optional fixed per-tier charge added on top of the per-unit tier amount (Stripe tiers[].flat_amount — e.g. a flat handling fee for the smallest-quantity band). A qualifier of the tier-price host, bound to one tier statement, as a numeral on a currency unit. Its magnitude is realised; the currency is the governed unit.

Tier flat fee is a price, given as an amount in a currency such as USD or EUR.

It is a qualifier of tier price — it has meaning only inside a tier price statement, one per statement, never on its own. It belongs with tier price to pricing — what it costs.

It is answered inside every tier price statement, not as a standalone question on a kind.

answered with: №number + unit — a number paired with a unit drawn from an exhaustive unit vocabulary.
value domain: Currencies — the vocabulary its answers are drawn from.
qualifier of: tier price — one per statement — it has meaning only inside that host's statement.

Answered inside every tier price statement — not a standalone slot on any kind.