Xacro unless property check -> error

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Running this file with roslaunch command, and passing the cam_serial and cam_index. But I'm getting error: Invalid roslaunch XML syntax: unbound prefix: line 3, column 0 The traceback for the exception was written to the log file

What is wrong?

<?xml version="1.0"?>
<launch>
   <xacro:property name="cam_serial" value="$(arg cam_serial)"/>
   <xacro:unless value="<21665943>">
   <
   <!-- Essential camera parameters -->
   <arg name="cam_serial"/>
   <arg name="cam_index"/>

   <!-- AOI Settings -->
   <arg name="aoi_width"  default="960" />
   <arg name="aoi_height" default="540" />
   <arg name="aoi_pos_x"  default="480" />
   <arg name="aoi_pos_y"  default="270" />

   <!-- Color calibration -->
   <arg name="red_gain" default="1.0" />
   <arg name="green_gain" default="1.09375" />
   <arg name="blue_gain" default="2.21075" />

   <!-- Additional parameters -->
   <arg name="auto_white_balance" default="false" />
   <arg name="bandwidth_limit" default="8000000" />
   <arg name="zoom" default="1" />
   <arg name="reverse_x"  default="false" />
   <arg name="reverse_y"  default="false" />

   <group ns="image$(arg cam_index)">
       <node name="cam$(arg cam_index)" pkg="basler" type="camera" respawn="true" respawn_delay="10"           output="screen">

          <!-- Some default parameters that probably don't need to be changed -->
          <param name="auto_exposure" value="false"/>
          <param name="auto_gain" value="false"/>
          <param name="gain" value="1.0"/>
          <param name="cam_serial" value="$(arg cam_serial)" unless="true"/>
          <param name="hardware_gamma" value="true" />
          <param name="frame_rate" value="1.0"/>
          <param name="exposure_time" value="25000.0"/>

          <!-- These parameters will probably be changed-->
          <param name="aoi_width"  value="$(arg aoi_width)" />
          <param name="aoi_height" value="$(arg aoi_height)" />
          <param name="aoi_pos_x"  value="$(arg aoi_pos_x)" />
          <param name="aoi_pos_y"  value="$(arg aoi_pos_y)" />
          <param name="zoom"       value="$(arg zoom)" />
          <param name="reverse_x" value="$(arg reverse_x)"/>
          <param name="reverse_y" value="$(arg reverse_y)"/>
          <param name="red_gain" value="$(arg red_gain)" />
          <param name="green_gain" value="$(arg green_gain)" />
          <param name="blue_gain" value="$(arg blue_gain)" />
          <param name="auto_white_balance" value="$(arg auto_white_balance)" /> 

          <!-- Remap trigger service and output topic -->
          <remap from="image_raw" to="raw"/>
          <remap from="trigger_camera" to="trigger_camera"/>
       </node>
    </group>
    >
 </xacro:unless>
 </launch>