C language: regexec returns not matching even the string matches the pattern

I use regex in the C language. I have the following code:

#include <regex.h>

static char input[] = "00001415_AXI_7_16";

static bool checkSn(char *input)
{
    regex_t regex;

    if (regcomp(&regex, "^\\d{1,8}_[A-Z]{3}_(\\*|\\d{1,3})_(\\*|\\d{1,3})$",
    REG_EXTENDED))
    {
        fprintf(stderr, "Error during creating regex\n");
        return false;
    }
    if (regexec(&regex, input, 0, NULL, 0))
    {
        return false;
    }
    return true;
}

I can compile the program without any warning. I can run the program, but the function returns false even the input string matches the regular expression, I tried it obviously at an online regular expression tester. Could you please help me where is a mistake?
Thank you in advance.

I tried few flags for the regcomp function. I tried the regular expression without "^" and without "$" with the same result.

You compile with REG_EXTENDED flag. However, the current regular expression using is the basic regular expression syntax.

You can change the regular expression to use the extended syntax, or you can remove the REG_EXTENDED flag from the regcomp function call.

With extended version:

if (regcomp(&regex, "^[[:digit:]]{1,8}_[[:upper:]]{3}_(\\*|[[:digit:]]{1,3})_(\\*|[[:digit:]]{1,3})$",
REG_EXTENDED))
{
    fprintf(stderr, "Error during creating regex\n");
    return false;
}

Or without:

if (regcomp(&regex, "^[0-9]\\{1,8\\}_[A-Z]\\{3\\}_\\(\\*\\|[0-9]\\{1,3\\}\\)_\\(\\*\\|[0-9]\\{1,3\\}\\)$",
0))
{
    fprintf(stderr, "Error during creating regex\n");
    return false;
}