Scala Play and Multi Project SBT Builds - scala

Question

I created a scala play project like this
activator new foo play-event-sourcing-starter
the project was generated successfully and I can go inside and easily compile and run the app.
However what I want is that I should have a multi project sbt build. I googled and found this https://www.playframework.com/documentation/2.5.x/SBTSubProjects
But this is not the same as what I want because here they have play as the root project. whereas what I want is that I have an empty root project with a build.sbt file and then multiple "peer" projects. One of them is play.
So I changed the steps to
mkdir -p LearnPlay/project
cd LearnPlay
activator new foo play-event-sourcing-starter
Now I went inside foo and moved the build.sbt to the LearnPlay directory. I also moved the build.properties and plugins.sbt files into LearnPlay/project folder.
I edited the build.sbt file so that the root project becomes
lazy val root = (project in file("foo")).enablePlugins(PlayScala)
However now sbt cannot compile the project anymore and it cannot find any of the play framework dependencies.
sbt.ResolveException: unresolved dependency: com.typesafe.play#play-server_2.10;2.5.9: not found
unresolved dependency: com.typesafe.play#play-netty-server_2.10;2.5.9: not found
unresolved dependency: com.typesafe.play#play-logback_2.10;2.5.9: not found
unresolved dependency: com.typesafe.play#play-test_2.10;2.5.9: not found
unresolved dependency: com.typesafe.play#play-omnidoc_2.10;2.5.9: not found
at sbt.IvyActions$.sbt$IvyActions$$resolve(IvyActions.scala:313)
These are the contents of my plugins.sbt file. The resolver is defined correctly so I am not sure why sbt will not be able to find the dependencies after the file was moved from sub-project to root project. it was able to resolve everything when the file was in the project directory of the foo project.
resolvers += "Typesafe repository" at "http://repo.typesafe.com/typesafe/releases/"
// The Play plugin
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.5.9")
// web plugins
addSbtPlugin("com.typesafe.sbt" % "sbt-digest" % "1.1.0")

Answer 1

The thing that gave me some ideas what's the problem there is:
unresolved dependency: com.typesafe.play#play-server_2.10;2.5.9: not found
Aren't you surprised, that sbt tries to download the version of play server for Scala 2.10, which doesn't exist for Play 2.5.x, since it's already out of lifecycle.
In my projects this is happening, if I'm not specifying scala version in build.sbt or set it to the 2.10, e.g.
lazy val root = (project in file("foo")).settings(
scalaVersion := "2.10.6",
so, I think you just need to add scalaVersion parameter and set it to something from 2.11.x or 2.12.x