Multi Instance

Hi everyone,
I would like to have a second instance of the sensor_gnss_relative message. Can someone help me how to do this? I have two gps connected to the pixhawk 4 and I can see sensor_gps0 and sensor_gps1 in the listener. sensor_gnss_relative_s is defined in the gps.cpp file with: uORB::PublicationMulti<sensor_gnss_relative_s>_sensor_gnss_relative_pub{ORB_ID(sensor_gnss_relative)};
So why does it not work?