Shopify Payments now provides an bank references on paid payouts.
Bank references are unique identifiers for payouts that our partners create to help you track missing or delayed payouts. If an expected payout hasn’t settled in your bank account but is marked as paid on Shopify, you can contact your bank for an update and provide the bank reference.
Simply go to Finances > Payouts > Payout Details (click on the payout) and you'll see the bank reference.