'This dependency' ? You mean paypal-core
? It's on maven as you can see, so all you need is to copy artifact from SBT tab: "com.paypal.sdk" % "paypal-core" % "1.5.2"
and add it to your project/Build.scala
file as described in Play doc in the Managed dependencies section.
Don't forget to perform play clean
play update
and eventually play yourIDE
after all