Returns the reward coupons issued to a validator, newest first. Canton pays validators
by issuing a coupon per reward round; the validator then claims it, converting it to
Canton Coin. This endpoint reports the coupons, which is the earnings record.

Filter status=claimable for rewards still available to claim — the practical use is
noticing that claims have stopped running.

Three limits to understand before relying on this.

status: settled does not distinguish a claim from a lapse. The ledger offers separate
choices for the validator claiming a coupon and for the network expiring an unclaimed
one, and both simply archive the record. A settled coupon may therefore represent
revenue collected or revenue lost, and this endpoint cannot tell you which.

Reward rounds themselves are not exposed. The round number is reported as issued, but
round timing and issuance rates are held in records this API does not serve, so a
round number cannot be turned into a date or a rate here.

Coupon amounts are fixed, but Canton Coin balances are not — a Canton Coin holding
carries a per-round decay rate and loses value as rounds pass. Do not sum coupon
amounts and treat the result as a current balance; it is cumulative gross issuance,
not holdings.