Use GET on /account/:id/interest/transactions with an interestMonth query value in YYYY-MM format to retrieve the account's interest credit and backup withholding transactions for a calendar month. Month boundaries use UTC−07:00, and future calendar months are rejected. The response separates posted (settled) transactions from pending ones; transactions in any other status are omitted. Rows use the same shape and visibility rules as Get Transactions, and the whole month is returned in one response. Pending rows are not proof of payment. If interest is not enabled for the account, the endpoint returns HTTP 400 with error code ACCOUNT_INTEREST_NOT_ENABLED.