Install_app('path to .apk') is not working

Hey all,
I’m using appium to automate some apps on real android device…The device is connected to selenium hub.
Appium 1.7.1
gem : appium_lib (9.6.1)
gem : selenium-webdriver (3.8.0)
Selenium build info: version: ‘3.7.1’, revision: ‘8a0099a’
OS - CentOS 7

I want to use @driver.install_app(path to apk file) but it is not working for me

my sample code:
require ‘appium_lib’

opts_dut = {
caps: {
platformName: :android,
version: ‘7.0’,
deviceName: ‘S7’,
appPackage: ‘com.android.settings’,
appActivity: ‘com.android.settings.MainActivity’,
noReset: true,
autoLaunch: false,
automationName: ‘uiautomator2’
},
appium_lib: {
server_url: ‘http://127.0.0.1:4444/wd/hub’,
wait_timeout: 300,
wait_interval: 100,
newCommandTimeout: 3000
}
}
$T = {}
$T[‘DUT’] = Appium::Driver.new(opts_dut, true).start_driver

$T[‘DUT’].install_app(’/home/tester/apk_repo/FSS.apk’)

$T[‘DUT’].quit

And result:
Selenium::WebDriver::Error::UnknownError: An unknown server-side error occurred while processing the command. Original error: Could not proxy. Proxy error: Could not proxy command to remote server. Original error: 404 - undefined

HTTP] --> POST /wd/hub/session/757a9f71-3325-4dfd-9fb1-c1189521fc30/appium/device/install_app {“appPath”:"/home/tester/apk_repo/FSS.apk"}
[MJSONWP] Driver proxy active, passing request on via HTTP proxy
[debug] [JSONWP Proxy] Proxying [POST /wd/hub/session/757a9f71-3325-4dfd-9fb1-c1189521fc30/appium/device/install_app] to [POST http://localhost:8200/wd/hub/session/0fa4c1c4-94e1-45c0-bf1e-3bd0f53df509/appium/device/install_app] with body: {“appPath”:"/home/tester/apk_repo/FSS.apk"}
[MJSONWP] Encountered internal error running command: Error: Could not proxy. Proxy error: Could not proxy command to remote server. Original error: 404 - undefined
at doJwpProxy$ (…/…/…/lib/mjsonwp/mjsonwp.js:384:13)
at tryCatch (/usr/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:67:40)
at GeneratorFunctionPrototype.invoke [as _invoke] (/usr/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:315:22)
at GeneratorFunctionPrototype.prototype.(anonymous function) [as throw] (/usr/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:100:21)
at GeneratorFunctionPrototype.invoke (/usr/lib/node_modules/appium/node_modules/babel-runtime/regenerator/runtime.js:136:37)
[HTTP] <-- POST /wd/hub/session/757a9f71-3325-4dfd-9fb1-c1189521fc30/appium/device/install_app 500 17 ms - 274

Please anybody has any idea how to solve it?
note: I can’t put it into “appPackage:”

Thanks!