Which API can be used to create Service Package (ESLH and ESLL) related to Contract (EKKO and EKPO)

Hi,

Which API tin beryllium utilized successful S4 on-premise strategy to make Service Package (tables ESLH and ESLL) related to Contract (tables EKKO and EKPO). I'm trying to use API_SERVICE_CONTRACT_SRV but it is not moving arsenic expected, it's returning bare responses with presumption 200.