stack smashing detected but the char array is within limits

I am trying to understand what I am doing wrong. The input from keyboard is within the char array limits... even if the input is 8 chars long, it throws an error. it works fine as long as the char is 6 chars long.

This is my code (I can swear it worked until 1h ago)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "functions.h"
#define SLEN 81
#define FILE_NAME "../database.txt"
void add_members(char *name);
int main(void)
{   
    char name[SLEN], surname[SLEN], address[SLEN];
    unsigned int dob, start_date, end_date;
    add_members(&name[SLEN]);

    return 0;
}

void add_members(char *name)
{   
    FILE *file;
    if ((file = fopen(FILE_NAME, "a")) == NULL)
    {
        printf("cant open file %s\n", FILE_NAME);
        exit(EXIT_FAILURE);
    }

    fputs("Insert FIRST NAME: ", stdout);
    fgets(name, SLEN, stdin); // appears the problem to be here
    check_string(name); // this is defined in another file
    fputs(name, file);
    printf("Name added to database: %s\n", name);

    if (fclose(file) != 0)
        printf("error in closing file %s\n", FILE_NAME);
    printf("File: %s closed\n", FILE_NAME);
}

add_members(&name[SLEN]);

That is not correct because &name[SLEN] is the byte after the end of the array. What is needed is the start of the array.

add_members(name); or add_members(&name[0]);