For Referenced Payment payment method there aren’t any test data available, but you can see how it works with the payment flow given below.
Referenced Payment Payment Flow
The Customer enters his email address.
The customer selects his preferred payment method from the list.
The customer receives a voucher containing the payment details and a barcode. He needs to print the voucher with the barcode and pay it at any branch of Bancolombia or Banco de Occidente in the country.
Upon completion of the payment flow, the customer is redirected back to your ReturnURL.