DEX v1 pays the referrer fee directly inside each swap transaction. The rate is fixed at 0.1 % and the specified referrer_address receives the tokens immediately.
Track payouts using the Stats & Vaults REST API:
GET /v1/stats/fee_accruals – shows all operations leading to fee accrual for the referrer, filterable by period
GET /v1/stats/fee_withdrawals – lists withdrawals from the referrer's vaults by period
GET /v1/stats/fees – returns aggregated referral fee information such as total accrued USD value
See the Omniston referral fees guide (remember: although the guide focuses on Omniston, the linked paragraph explains DEX V1 referral fees in detail). Full API docs are available in the Swagger UI.