I am using route API :computeRoutes

This is the body I am sending

"origin": {
"address": "Delhi"
 },
 "destination": {
 "address": "Prayagraj"
 },
 "travelMode": "TRANSIT",
 "transitPreferences": {
 "allowedTravelModes": ["TRAIN", "RAIL"]
 },
 "computeAlternativeRoutes": true
 }

But I am not getting train route in the API, just the driving route How can I get the train route

If I am selecting the same destination then google maps is giving the train info properly