How to resolve my Timer Interrupt issue
Try this instead.

#include “TimerOne.h”
bool val=0;
void setup()
{
    pinMode(13, OUTPUT);
    Timer1.initialize(500000); // initialize timer1, and set a 1/2 second period
    Timer1.attachInterrupt(callback); // attaches callback() as a timer overflow interrupt
}

void callback()
{
    val=!val;
}

void loop()
{
    digitalWrite(13,val);
}