Realloc invalid pointer depending on where I initialize the variable in C

I'm stuck doing something that shouldn't be that hard, I want to add element to my char** but when I try to add some elements to my first array then some to my second sometime it doesn't work depending of where I declare my second array ...

The error code I have is : "realloc(): invalid pointer\nAbandon (core dumped)"

int main(void)
{
   char *a = "aaa";
   char *b = "bbb";
   char *c = "ccc";
   char *d = "ddd";
   char *e = "eee";

   char **s1 = malloc(sizeof(char*));
   if(s1 == NULL) printf("wkwk\n");
   *s1 = NULL;
   int size1 = 0;

   char **s2 = malloc(sizeof(char*)); // the problematic line is here
   if(s2 == NULL) printf("blbl\n");
   *s2 = NULL;
   int size2 = 0;

   array_add(s1,a,&size1);
   array_add(s1,b,&size1);
   array_add(s1,c,&size1);

   array_add(s2,d,&size2);
   array_add(s2,e,&size2);

   // printing

   return 0;
}

void array_add(char **array,char *string,int *nb_elem)
{
   array = realloc(array,sizeof(array)+sizeof(string));
   if(array == NULL) exit(EXIT_FAILURE);
   array[*nb_elem] = malloc(sizeof(string));
   if(array[*nb_elem] == NULL) exit(EXIT_FAILURE);
   strcpy(array[*nb_elem],string);
   *nb_elem = *nb_elem + 1;
}

I don't know why but if I malloc s2 after the first array_add(s1,a,&size1) it works without problem (I haven't tried with more array tho).