C Realloc Error - Dynamic Array in struct - c

Question

first of all thank you so much for trying to help me, or at least have a look at my problem and maybe tell me, what I am doing wrong.
Ok, so I've recently encountered the problem that realloc() throws a segmentation fault error, when used to extend an array in a typedef struct, or at least so it does in my case.
I've tried to find the solution online, on this webpage and on other ones, but sadly I couldn't seem to find one. Which is why I really hope that one of you would be so kind to help me.
Thank you so much in advance,
Matthias
Btw. here I appended the code that is providing me errors.
typedef struct dict_int {
int* size;
char** keys;
int* values;
} dict_int;
This is my struct. And below is the function (add_int()), which is making problems... ;(
void add_int(dict_int* dictionary, int len, ...) {
va_list valist;
va_start(valist, len);
int di_size = dictionary->size[0];
for(int i = di_size-1; i < di_size-1+len; i++) {
dictionary->keys[i] = va_arg(valist, char*);
dictionary->values[i] = va_arg(valist, int);
printf("Change [Size]: %d -> ", dictionary->size[0]);
dictionary->size[0]++;
printf("%d\n", dictionary->size[0]);
if((dictionary->keys = (char**) realloc(dictionary->keys, dictionary->size[0] * 4 + 4))
!= NULL) {
printf("Worked out!");
} else
printf("Didn't work!");
if((dictionary->values = (int*) realloc(dictionary->values, dictionary->size[0] * 4 + 4))
!= NULL) {
printf("Worked out!");
} else
printf("Didn't work!");
}
va_end(valist);
}
And here's how I used it in the main() function:
int main(int argc, char* argv[]) {
printf("\n - !Program has started! - \n");
dict_int dictionary = Dict_int(2, "first", 0, "second", 1);
printf("\nDictionary-Size: %d\n", dictionary.size[0]);
printf("Dictionary: %s: %d\n", dictionary.keys[0], dictionary.values[0]);
printf("Dictionary: %s: %d\n", dictionary.keys[1], dictionary.values[1]);
printf("Dictionary: first: %d\n", get_int(&dictionary, "first"));
add_int(&dictionary, 1, "third", 2);
add_int(&dictionary, 1, "uno", 1);
/* printf("uno: %d\n", get_int(&dictionary, "uno"));
printf("third: %d\n", get_int(&dictionary, "third"));
printf("\n - !Program has finished! - \n");*/
return 0;
}
Also, the code works out alright, if I only call add_int() once, so if I only were to add one element to my dict_int it wouldn't throw an error, which is why I'm guessing that it has something to do with the memory...
Also, I tried to remove all the pieces of add_int() that included a realloc(), in order to prove my theory, and without realloc() it seems to work just fine...
So, just know that I'm very grateful to you, for just reading trough this question, and I'd be even more grateful, if you were so kind, and tried to tell me what I'm doing wrong, since sadly, I can't figure out. - Matthias