Writing into a malloc string

I'm new to C programming language, and malloc precisely. So I created this program to take arguments from argv and put them all in a single string, separated by spaces(on line 32). But when I run it, everything works out, but there seems to be no spaces inserted as desired in the code below.

When I tried commenting, line 28: buffer[t] = argv[str][i]; the spaces appear.

I also tried casting: malloc(buffSize) to (char*) before assigning it to buffer to just see if anything changes¿¿. But nothing.

Please I'd be glad if someone can clear me out on what's going on. Thanks in advance 🙏🏼

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int str = 0, i = 0, t = 0, letterCount = 0, buffSize;
    char *buffer;
    char *argv[] = {"hello", "me", "too"};
    int argc = 3;

    while (str < argc)
    {
        while (argv[str][i++])
            letterCount++;
        str++;
        i = 0;
    }
    buffSize = letterCount + argc + 1;
    str = 0;
    buffer = (char*) malloc(buffSize);
    if (!buffer)
        return (NULL);
    while (str < argc)
    {
        while (argv[str][i] != '\0')
        {
            buffer[t] = argv[str][i];
            t++;
            i++;
        }
        buffer[t] = ' ';
        str++;
        i = 0;
    }
    printf("%s", buffer);
    return (0);
}