From 2022-06-22 we change how we handle buy price for non-default pricelists in API.
You can set buy price of product in pricelist update endpoint.
Via API this field can be set for all of your pricelists but only default pricelist can be set in eshop administration.
From the mentioned date we will ignore this value in non-default pricelists and in our response you will find null value.
I case of different purchase price need we warmly recommend split your products into two separate products.
We belive that this change will not harm your implementations.