You have to create a client jar which contains all necessary interfaces and also the parameter classes which might be passed to the methods of the interface.
In your example you need to put
- VoidRemittanceService
- VoidRemittanceServiceRemote
- PaymentResponse
into the client jar.
The implementing classes of the remote interfaces are not necessary within the client jar.
Of course you can also make a copy and put them into the client project. But this is not good practice since you have to make changes of the interface always twice. Additionally you must be sure that the client interfaces are compiled with the same JRE Version as the server jar. Else there could be problems.
Good practice is to create an additional project which contains shared code means which will be used by server and client. This project can be referenced by the server project and the client project. In this way changes of the shared code influence directly the server and the client side.