Manage dependencies with sbt & IntelliJ IDEA - scala

Question

I'm working on a back-end project using for the first time Scala and the Play Framework with IntelliJ IDEA.
I've been reading a lot of documentation and topics:
SBT Library dependencies doc
IntelliJ support post
Another post from stackoverflow
I can't understand how to import dependencies.
When I try to append a new dependency, IntelliJ underlines it and shows either "Unknown artifact. Not resolved or indexed" or a log shows up and says "SBT unknown import".
Every dependency I add is from the Maven Repository.
Here is the build.sbt file:
name := "server"
version := "1.0"
lazy val `server` = (project in file(".")).enablePlugins(PlayScala)
resolvers += "scalaz-bintray" at "https://dl.bintray.com/scalaz/releases"
resolvers += "Akka Snapshot Repository" at "http://repo.akka.io/snapshots/"
resolvers := ("Atlassian Releases" at "https://maven.atlassian.com/public/") +: resolvers.value
scalaVersion := "2.12.2"
libraryDependencies ++= Seq(
jdbc,
ehcache,
ws,
specs2 % Test,
guice,
"org.mongodb.scala" %% "mongo-scala-driver" % "2.1.0",
"com.mohiva" %% "play-silhouette" % "5.0.2",
"com.mohiva" %% "play-silhouette-password-bcrypt" % "5.0.2",
"com.mohiva" %% "play-silhouette-crypto-jca" % "5.0.2",
"com.mohiva" %% "play-silhouette-persistence" % "5.0.2",
"com.mohiva" %% "play-silhouette-testkit" % "5.0.2" % "test"
)
unmanagedResourceDirectories in Test <+= baseDirectory ( _ /"target/web/public/test" )

Answer 1

These dependencies were specified using a shorthand that is defined by the Play plugin:
jdbc,
ehcache,
ws,
specs2 % Test,
guice
So for them to work, be sure to include a line like the following in an .sbt file in the project directory:
addSbtPlugin("com.typesafe.play" % "sbt-plugin" % "2.6.10")
That should fix your problem.
Bonus tip: No need for the following lines, and because each additional resolver slows down SBT, you should delete them:
resolvers += "scalaz-bintray" at "https://dl.bintray.com/scalaz/releases"
resolvers += "Akka Snapshot Repository" at "http://repo.akka.io/snapshots/"
resolvers := ("Atlassian Releases" at "https://maven.atlassian.com/public/") +: resolvers.value