hello. I am trying to spawn two similar robot at a time and the following is the launch file I wrote. the problem is that only first robot appears in gazebo and in the log file I got this error :"[rosout][INFO] 2022-09-02 13:56:55,036: Spawn status: SpawnModel: Failure - entity already exists." is there any specific setting for gazebo that can solve the problem of the problem has its roots somewhere else?

<?xml version="1.0" encoding="UTF-8"?> <!-- START GAZEBO -->

<!-- launch the simulator world -->
<arg name="debug" default="false"/>
<arg name="gui" default="true"/>
<arg name="headless" default="false"/>
<arg name="pause" default="false"/>
<arg name="world" default="simulation" />
<include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="world_name" value="$(find rosbot_simulation)/worlds/$(arg world).world"/>
    <arg name="debug" value="$(arg debug)" />
    <arg name="gui" value="$(arg gui)" />
    <arg name="paused" value="$(arg pause)"/>
    <arg name="use_sim_time" value="true"/>
    <arg name="headless" value="$(arg headless)"/>
    <arg name="verbose" value="true"/>
</include>

<!-- BEGIN ROBOT 1-->

<!-- SPAWN ROBOT --> <!-- Robot state publisher--> -->

<!-- BEGIN ROBOT 2--> <!-- SPAWN ROBOT --> <!-- Robot state publisher--> -->