Regla: CAD15a, Rechazo: Código de divisa inválido

Question

Hello !
I'm trying to send a Credit Note to SendBillSync (in test mode, using the test endpoint https://vpfe-hab.dian.gov.co/WcfDianCustomerServices.svc?wsdl), and I receive the error:

"Regla: CAD15a, Rechazo: Código de divisa inválido"

Although my xml contains:
<cbc:DocumentCurrencyCode listAgencyID="6" listAgencyName="United Nations Economic Commission for Europe" listID="ISO 4217 Alpha">COP</cbc:DocumentCurrencyCode>
Does anyone knows what I'm missing ? :)