Pausing simulation for reinforcement learning does not work

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Dears, I am trying to train my turtlebot2 using openAI ros package. The problem I am facing is that I can't unpause and pause the simulation at each timestep.

    self.gazebo.unpauseSim()
    self.move_base(linear_vel, angular_vel, time_step=self.time_step)
    self.gazebo.pauseSim()

The above code odes not work. However, I need my simulation which has actors (pedestrians) to pause after each time step. I tried serviceProxy which works at first, I mean if the simulation is paused and I wanted to unpause it, but the pause service is not working again. any help please.