SAME SUPPLIER REFERENCE CODE FOR SEVERAL PRODUCTS

Hi
I have this case using “buying prices” module.

I have the reference code of the product/supplier what can be related to several products registered in the system . But the system no alow me to add that info for the second product.
e.g.
supplier A with ref BB linked to Product 123 ( OK )
supplier A with ref BB linked to Product 456 ( dolibar no alllow it )
supplier A with ref BB linked to Product 789

How could I set up the system to have the relation Product + Supplier + reference code in that module ?

Thanks in advance,