can you clarify whay you mean by "application APIs"? Dynatrace has many different kinds of APIs.
If you are talking about the relationships of your Applications, you can get the Application layer of the Smartscape by using the Topology and Smartscape API: https://www.dynatrace.com/support/help/dynatrace-a...
If by application you mean your RUM data, you can use the User Sessions API: https://www.dynatrace.com/support/help/dynatrace-a...
If you mean, can you view the transactions using your application APIs, the answer is yes. They would be considered one or more services and should be visible under the "Transactions & services" menu item.