This illustrates retrieving related data using the include argument:

    include=OrderList,OrderList.OrderDetailList,OrderList.OrderDetailList.Product

See: https://apilogicserver.github.io/Docs/API-Multi-Table/

See: 

curl -X GET "http://localhost:5656/api/Customer/ALFKI/?\
include=OrderList%2COrderList.OrderDetailList%2COrderList.OrderDetailList.Product&\
fields%5BCustomer%5D=Id%2CCompanyName%2CContactName%2CContactTitle%2CAddress%2CCity%2CRegion%2CPostalCode%2CCountry%2CPhone%2CFax%2CBalance%2CCreditLimit%2COrderCount%2CUnpaidOrderCount%2CClient_id" \
  -H 'accept: application/vnd.api+json' \
  -H 'Content-Type: application/vnd.api+json'