Be sure that N3FJP FD Logger has the API enabled.
Configure both WSJT-X and JTAlert for Field Day.
In WSJT-X enter a call in the DX CAll window.
Click Log QSO
In the QSO entry window fill in both the exchanges (1E EPA) and click OK.
The QSO should log in N3FJP FD Logger.
Hope that helps.