referrerClient.kt

val referrerClient: InstallReferrerClient = InstallReferrerClient.newBuilder(this).build()
        referrerClient.startConnection(object : InstallReferrerStateListener {

            override fun onInstallReferrerSetupFinished(responseCode: Int) {
                when (responseCode) {
                    InstallReferrerClient.InstallReferrerResponse.OK -> {
                        // Connection established
                        val response: ReferrerDetails = referrerClient.installReferrer
                        Log.d("TAG",response.installReferrer)
                        referrerClient.endConnection()
                    }
                    InstallReferrerClient.InstallReferrerResponse.FEATURE_NOT_SUPPORTED -> {
                        // API not available on the current Play Store app
                        mReferrerTrigger.onNext(Pair(false, ""))
                    }
                    InstallReferrerClient.InstallReferrerResponse.SERVICE_UNAVAILABLE -> {
                        
                        // Connection could not be established
                    }
                    else -> {
                        
                    }
                }
            }

            override fun onInstallReferrerServiceDisconnected() {
                // Try to restart the connection on the next request to
                // Google Play by calling the startConnection() method.
            }
        })