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The rosservice call <service_name> <request> is in fact a python script: https://github.com/ros/ros_comm/blob/melodic-devel/tools/rosservice/src/rosservice/__init__.py

So I would suggest that you are either not in the same network setup with your other python script or you misspelled the used .srv or service_name. There is no point why the ros_comm cli tools work from the same shell and a custom written python client would not.

Maybe you want to check out the new Micro-ROS for ROS2: https://micro-ros.github.io/

rosserial is known to be a bit buggy on Arduinos. At least to my knowledge. Consider upgrading to a more powerful STM32 or Teensy. They have faster clock rates that helps to come up with more complex protocols etc.

You can see here a similar situation where we believed that there was some error between cli and a python client node: https://github.com/micro-ROS/zephyr_apps/issues/4#issuecomment-631409686

In the end it was just a wrong spelled server_name ..