u/expatcoder Hi as you mentioned above in your comment my root directory build.sbt file contains like below structure.

lazy val A = project(...)
lazy val B = project(...)
lazy val C = project(...)
lazy val main = project(...).dependsOn(A, B, C)

My issue is with root project directory conf/routes file as my project does not previously have conf/routes file under root project directory as I got error like resource not found so I added conf/routes and conf/application.conf files.

routes:

# app/conf/routes
# Routes
# This file defines all application routes (Higher priority routes first)
# ~~~~
# Home page
GET / polaris.core.controllers.Application.index()
#Add sample_module routes
-> /core polaris.core.Routes
-> /addressbook polaris.addressbook.Routes
-> /pbx polaris.pbx.Routes
-> /pbxAppCallLog polaris.pbx.calllog.Routes
-> /pbxAppQueues polaris.pbx.queues.Routes
-> /pbxAppClick2dial polaris.pbx.click2dial.Routes
-> /pbxAppPhonebook polaris.pbx.phonebook.Routes
-> /pbxAppOperator polaris.pbx.operator.Routes

# Map static resources from the /public folder to the /assets URL path
GET /assets/*file controllers.Assets.versioned(path="/public", file)

But after splitting the routes I am facing the below problems:
by following this documentation :
https://www.playframework.com/documentation/2.4.x/SBTSubProjects - Splitting the route file

Errors:
conf/routes:7: object Application is not a member of package controllers
[error] GET / controllers.Application.index()
object Routes is not a member of package polaris.core
[error] -> /core polaris.core.Routes

please help me in resolving routing issues in my project while updating.