Testing Estimation Question:

The first step in FPA is to define the boundary. There are two types of major boundaries:

Internal Application Boundary
External Application Boundary

The external application boundary can be identified using the following litmus test:

Does it have or will it have any other interface to maintain its data, which was not developed by you?.
Does your program have to go through a third party API or layer? In order for your application to interact with the tax department application your code has to interact with the tax department API.
The best litmus test is to ask yourself if you have full access to the system. If you have full rights to make changes then it is an internal application boundary, otherwise it is an external application boundary.