Technical documentation and examples of idealo APIs can be found here:
API Checkout order retrieval (Merchant Order API V2): https://cdn.idealo.com/folder/Direktkauf/documentation/merchant-order-api-v2.html
API offer transmission (PartnerWebservice 2): https://import.idealo.com/docs/
API idealo business: https://business.idealo.com/en/direct/mi/settings/api-client#top