Problem with running related scripts via systemd

I tried to run three related script automatically (launcher,set-app,checkapp.py) using systemd timer and systemd service, first script check the python script (gui app) if he already running, after that he restart the python gui app, my problem is when i trying to run systemd service, it close the gui app

this is the first script (launcher):

#!/bin/bash
/usr/share/checkapp/set-app 
exit 0

and this is the second one (set-app):

#!/bin/bash
CHECK_PRO="$(ps -ef | grep '[p]ython3 /usr/share/checkapp/checkapp.py' | awk '{print $2}')"
if [ "${CHECK_PRO}" != "" ]; then
    kill -9 $CHECK_PRO
    python3 /usr/share/checkapp/checkapp.py show &
fi
exit 0

and this is the last one (checkapp.py):

#!/usr/bin/env python3


import os
import signal
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk as gtk
from gi.repository import AppIndicator3 as appindicator
gi.require_version('Gtk', '3.0')

APPINDICATOR_ID = 'checkapp'
app_ico = '/usr/share/checkapp/logo.svg'

def main():
    indicator = appindicator.Indicator.new(APPINDICATOR_ID, os.path.abspath(app_ico), appindicator.IndicatorCategory.SYSTEM_SERVICES)
    indicator.set_status(appindicator.IndicatorStatus.ACTIVE)
    indicator.set_menu(build_menu())
    gtk.main()

def build_menu():
    menu = gtk.Menu()
    software_cen = gtk.MenuItem('Software Center')
    software_cen.connect('activate', software_center)
    menu.append(software_cen) 
    menu.show_all()
    return menu

def software_center(source):
    os.system('pkexec /usr/sbin/synaptic')
if __name__ == "__main__":
    signal.signal(signal.SIGINT, signal.SIG_DFL)
main()

and this is the checkapp.service file :

[Unit]
Description=checkapp
[Service]
ExecStart=/usr/share/checkapp/launcher

and this is checkapp.timer file:

[Unit]
Description=Running checkapp every 2 hour
RefuseManualStart=no                       
RefuseManualStop=no                       

[Timer]
OnBootSec=20
OnUnitActiveSec=120min
AccuracySec=1ms
Unit=checkapp.service

[Install]
WantedBy=timers.target