AR track alvar not finding any AR tags

edit

I am newbie in ROS and first time using ar_track_alvar. I am using ubuntu 18.04, ROS melodic and a Realsense D435i camera for AR tag detection. The ros file I am using is below

<launch>
<arg name="marker_size" default="4.4" />
<arg name="max_new_marker_error" default="0.08" />
<arg name="max_track_error" default="0.2" />
<arg name="cam_image_topic" default="/camera/color/image_raw" />
<arg name="cam_info_topic" default="/camera/color/camera_info" />
<arg name="output_frame" default="/camera_link" />

<node name="ar_track_alvar" pkg="ar_track_alvar" type="individualMarkersNoKinect" respawn="false" output="screen">
    <param name="marker_size"           type="double" value="$(arg marker_size)" />
    <param name="max_new_marker_error"  type="double" value="$(arg max_new_marker_error)" />
    <param name="max_track_error"       type="double" value="$(arg max_track_error)" />
    <param name="output_frame"          type="string" value="$(arg output_frame)" />

    <remap from="camera_image"  to="$(arg cam_image_topic)" />
    <remap from="camera_info"   to="$(arg cam_info_topic)" />
</node>

</launch>

The marker I am usning is the 26 AR marker link text

I tried to find solutions and one thing I frequently see is calibrating the camera. I have no idea how to do that either. The /ar_track_alvar/Pose does not show any message and TF also does not show up

Can anyone please help me in this regard ? Thanks in advance