no matching function for call to

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Hey everybody, I'm working on a node that uses a service to repeat a string a variable amount of times. for this i made the following srv file:

string text
int32 nrOfDuplicates
---

this will be processed by the following C++ code:

#include "ros/ros.h"
#include "std_msgs/String.h"
#include "std_msgs/Int32.h"
#include <string>

void multiply (std_msgs::String::ConstPtr   & str, std_msgs::Int32      & var){
int amount = var.data;
    for(int i = 0 ; i < amount ; i++)
    {
        ROS_INFO("%s", str->data.c_str());
    }
 ROS_INFO("/n");
}

int main(int argc, char **argv)
{
  ros::init(argc, argv, "add_duplicates");
  ros::NodeHandle n;
  ros::ServiceServer service = n.advertiseService("add_duplicates", multiply);
  ros::spin();

  return 0;
}

however, when i use catkin_make to compile the node, i get the following error:

/home/osboxes/catkin_ws/src/final/src/duplicator.cpp: In function ‘int main(int, char**)’:
/home/osboxes/catkin_ws/src/final/src/duplicator.cpp:19:77: error: no matching function for call to ‘ros::NodeHandle::advertiseService(const char [15], void (&)(std_msgs::String_<std::allocator<void> >::ConstPtr&, std_msgs::Int32&))’
   ros::ServiceServer service = n.advertiseService("add_duplicates", multiply);
                                                                             ^

I was considering that it is looking for a function that uses a string and int32 instead of the Std_msgs counterpart, but i'm a total ROS newbie and am not sure if this is true, or how to write it otherwise.

all help is appreciated!