I am trying to make a substitution cipher but it seems to have a segmentation fault when argc does not equal 2

#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>

bool error(void);

int main(int argc, string argv[])
{
    string key = argv[1];
    int n = strlen(key);
    printf("argc = %in n = %in", argc, n);
    if (argc != 2 || n != 26)
    {
        return error();
    }
    for (int i = 0; i < n; i++)
    {
        key[i] = toupper(key[i]);
        if (key[i] < 'A' || key[i] > 'Z')
        {
            return error();
        }
    }
    for (int i = 0; i < n; i++)
    {

        for (int j = i + 1; j < n; j++)
        {
            if (key[i] == key[j])
            {
                return error();
            }
        }
    }
    string text = get_string("plaintext: ");
    n = strlen(text);
    for (int i = 0; i < n; i++)
    {
        if (isupper(text[i]))
        {
            text[i] = key[text[i] - 65];
        }
        else if(islower(text[i]))
        {
            text[i] = tolower(key[text[i] - 97]);
        }
    }
    printf("ciphertext: %sn", text);
}

bool error(void) {
    printf("Usage: ./substitution keyn");
    return 1;
}

tried printf to display the parameters of main but exited with segmentation fault
my post is mostly code and the bot is saying that i need to add more details but not sure what else to add can someone advise