Hello Edgar,
Is the purchase requisition type 'RV'? If yes, this is standard that only one contract should be created with reference to this PR.
If you test similar scenario by T-code ME31K, you might get message 06053 for the second contract. On the Reference to PReq pop up screen, you can try to untick the 'Open Only' field (RM06E-OFFBA), then you can create the second contract.
But there is no RM06E-OFFBA for BAPI_CONTRACT_CREATE. So it is not possible to create the second contract with the BAPI.
Best regards,
Kevin