Dynamic_Reconfigure: Set Parameter Value from C++ Code

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Hello - I am new to ROS. I am using Ros Noetic on Ubuntu 20.04.

I followed the dynamic_reconfigure tutorial and have dynamic_reconfigure parameters working. I have 1 parameter which is defined as a bool_t in the .cfg file, so in the rqt_reconfigure GUI it appears as a checkbox. In my C++ code, if the parameter value is true (i.e checkbox is checked) I will save data to a file. Once the data is saved, the C++ code should set the parameter value to false so the checkbox in the rqt_reconfigure GUI gets unchecked.

In order to change the value of a dynamic reconfigure parameter in C++ code, I followed these instructions and information in this FAQ. This is my code:

#include <dynamic_reconfigure/BoolParameter.h>
#include <dynamic_reconfigure/Reconfigure.h>
#include <dynamic_reconfigure/Config.h>

dynamic_reconfigure::ReconfigureRequest srv_req; 
dynamic_reconfigure::ReconfigureResponse srv_resp; 
dynamic_reconfigure::BoolParameter bool_param; 
dynamic_reconfigure::Config conf;

bool_param.name = "save_data_to_file";
bool_param.value = false;    // I also tried setting this to 0 instead of false with same results
conf.bools.push_back(bool_param);

srv_req.config = conf;
ros::service::call("/myNodeName/set_parameters", srv_req, srv_resp);

The ros::service::call line hangs. I have print statements before and after that line and never see the print that is after it.

From a command line, I can run this command and it works so I'm certain I'm using the correct node name, the correct parameter name etc:

rosrun dynamic_reconfigure dynparam set /myNodeName save_data_to_file false

Any suggestions as to why the ros::service::call in the C++ code hangs? Watching the values of the parameter from a command line, the ros::service::call does not change the value of the parameter.

Thanks in advance!

EDIT #1: This is my C++ code cut down to the basics. When I run it, I can see the "BEFORE" print statement, but not the "AFTER". The value of save_data_to_file never changes.

#include <unistd.h>
#include "ros/ros.h"
#include "dynamic_reconfigure/server.h"
#include "test/dynamicParamsConfig.h"
#include <dynamic_reconfigure/BoolParameter.h>
#include <dynamic_reconfigure/Reconfigure.h>
#include <dynamic_reconfigure/Config.h>

void callback(test::dynamicParamsConfig &config, uint32_t level) {
   ROS_INFO("Reconfigure request : save:%i number: %i", 
        config.save_data_to_file,
        config.num_to_save
        );

}

int main(int argc, char **argv)
{

   ros::init(argc, argv, "publisher");
   ros::NodeHandle nh; 

   dynamic_reconfigure::Server<test::dynamicParamsConfig> server;
   dynamic_reconfigure::Server<test::dynamicParamsConfig>::CallbackType f;
   f = boost::bind(&callback, _1, _2);
   server.setCallback(f);

   while (ros::ok())
   {
      for (int i=0; i < 15; ++i) {

         ROS_INFO("Loop: %i", i);
         if (i==9) {
            dynamic_reconfigure::ReconfigureRequest srv_req;
            dynamic_reconfigure::ReconfigureResponse srv_resp;
            dynamic_reconfigure::BoolParameter bool_param;
            dynamic_reconfigure::Config conf;

            bool_param.name = "save_data_to_file";
            //bool_param.value = 0;  
            bool_param.value = false;
            conf.bools.push_back(bool_param);

            srv_req.config = conf;
            ROS_INFO("BEFORE");  // I see this print statement
            ros::service::call("/publisher/set_parameters", srv_req, srv_resp);
            ROS_INFO("AFTER");  // I never see this print statement
         }
         sleep(2);
         ros::spinOnce();
      }
   }
  return 0;
}