RE: How to create Rest API in x++
By the way, third-party system isn't the same as integration. That's just a source of data and an integration architect must decide how data will be fetched from there.
The architecture must respect capabilities of each system (therefore you can't design it before learning what APIs does F&O offer) all business requirements, including things like performance, reliability and security.
For example, you may want to build the architecture in a way that doesn't require both system running at the same and no direct communication between them. Let's say that the other system would put mesesages to a Service Bus Queue and a Logic App would monitor the queue and pass messages to F&O.