*.proto files are ignored

Question

Im trying to use protobuffers and scalaPB, i've added:

import com.trueaccord.scalapb.compiler.Version.scalapbVersion

libraryDependencies += "com.trueaccord.scalapb" %% "scalapb-runtime" % 
scalapbVersion % "protobuf"

PB.targets in Compile := Seq(
  scalapb.gen() -> (sourceManaged in Compile).value
)

and below lines to plugins.sbt

addSbtPlugin("com.thesamet" % "sbt-protoc" % "0.99.3")

libraryDependencies += "com.trueaccord.scalapb" %% "compilerplugin" % "0.5.47"

and .proto file under src/main/protobuf:

syntax = "proto3";

import "scalapb/scalapb.proto";
import "google/protobuf/wrappers.proto";

package actors;
message ExamplePROTO {
    double value = 1;
}

but using sbt compile nothing happens - class is not generated in target. File is ignored, because even with some typo in protobuf file project still compiles. Ive also tried to look at debug logs using

logLevel in Global := Level.Debug

but the only files .proto which are mentioned there are some internal ones like: /target/protobuf_external/google/protobuf/source_context.proto

How can I proceed with it? Can I get some more information what scalaPB is looking at?