Looking at your image, it looks like you are doing a direct flight to VIDP. Have you added a SID and a STAR? Only placing the destination airport as the ONLY waypoint won't do. You are best to add Depart Airport, a SID, Jetways and Waypoints, a STAR and an Approach (like an ILS runway) at the Destination Airport, or it looks like you won't see the magenta route on the Display.

Mind you, VIDP is listed as 3632nm away so it will still fly you there, even though the route is not displaying. ;)