SAP Message BBP_ES_ERP_INT006 - Ref. PR &1 item &2 cannot be selected, already used in E-Sourcing RFQ

Diagnosis
The system is set up to send specific requests for quotations (RFQs) tothe linked E-Sourcing system. You want to create a request for quotation(RFQ) by referencing a purchase requisition. The reference item you wantto adopt is already used as reference in an RFQ that has already beensent to the linked E-Sourcing system.
However, to avoid double procurement, it is not possible, to copy thisreference item to other RFQs.

Procedure
As this purchase requisition item is already being sourced by the linkedE-Sourcing system, select another reference item for the RFQ.