Waiting for service /gazebo/spawn_urdf_model. Gazebo doesn't find my model

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I am following a tutorial to build a custom robot in Ros. I followed in detail this tutorial: https://www.youtube.com/watch?v=uvPFD... I am trying to make my robot called "mrm" spawn in gazebo. When I try to launch the model no error messages are appearing but everything is stuck and this message appears in the terminal:

It appears it is searching for the model of the robot as reported by: https://answers.ros.org/question/3839...

If someone has some hints about how to solve this problem I would be very grateful.

I attach the link to my question on stackoverflow where I reported the launch file I am exploiting and the complete terminal message: https://www.google.com/url?sa=t&rct=j...

Lorenzo