Rviz: Global Status Error: Fixed frame [map] does not exist; Robot Model Error

[Kushagra-05]

I made a Nav2_Costmap2d plugin (had no problem in the build) (https://navigation.ros.org/plugin_tutorials/docs/writing_new_costmap2d_plugin.html#tutorial-steps)
& enabled it in Nav2_params.yaml as given in doc but when I run turtlebot in Rviz, the output is nowhere like it is mentioned, I don't see any any gradient.
Moreover, It gives errors like- Global Status Error: Fixed frame [map] does not exist & Robot Model Error

[faisalam1n]

Hi Khushagra, I'm getting the same error implementing multi-robot SLAM, following this video: https://www.youtube.com/watch?v=ndvwDFi-I3I
and this link: http://wiki.ros.org/turtlebot3_simulations
plz let me know if you find a solution. Thank You!