TOTP implementation using C++ and OpenSSL

I am trying to implement TOTP in C++ using OpenSSL. I know there are vast amounts of existing implementations; however, I would like to implement it myself.

Currently. I have the following code:

bool verifyTOTP(char* code, char* key, int codeLen, int keyLen) {
    if (codeLen != 6 || keylen != 20) {
        return false;
    }
    unsigned long long intCounter = floor(time(NULL)/30);
    char md[20];
    unsigned int mdLen;
    HMAC(EVP_sha1(), key, keylen, (const unsigned char*)&intCounter, sizeof(intCounter), (unsigned char*)&md, &mdLen);
    OPENSSL_cleanse(key, keylen);
    int offset = md[19] & 0x0f;
    int bin_code = (md[offset] & 0x7f) << 24
        | (md[offset+1] & 0xff) << 16
        | (md[offset+2] & 0xff) << 8
        | (md[offset+3] & 0xff);
    bin_code = bin_code % 1000000;
    char correctCode[7];
    snprintf((char*)&correctCode, 7,"%06d", bin_code);
    int compR = compHash(&correctCode, code, 6); // Compares the two char arrays in a way that avoids timing attacks. Returns 0 on success.
    delete[] key;
    delete[] code;
    if (compR == 0) {
        return true;
    }
    std::this_thread::sleep_for(std::chrono::seconds(5));
    return false;
}

This code does not give any error but fails to produce the correct TOTP, and therefore it returns false when the correct TOTP is verified.

For example, when running the below it should return true:

char* newKey = new char[20];
char* key = "aaaaaaaaaaaaaaaaaaaa";
memcpy(newKey, key, 20);
verifyTOTP(newKey, code, 6, 20);

Where code is the token from the TOTP Generator (when using the generator please ensure that the secret key is set to MFQWCYLBMFQWCYLBMFQWCYLBMFQWCYLB).

Can anyone spot where I went wrong? I have looked at how other people implemented it but could not find where the problem is.

Thank you so much for your attention and participation.

After dividing the Unix timestamp by 30, it is necessary to ensure that intCounter is big endian:

unsigned long long endianness = 0xdeadbeef;
if ((*(const uint8_t *)&endianness) == 0xef) {
  intCounter = ((intCounter & 0x00000000ffffffff) << 32) | ((intCounter & 0xffffffff00000000) >> 32);
  intCounter = ((intCounter & 0x0000ffff0000ffff) << 16) | ((intCounter & 0xffff0000ffff0000) >> 16);
  intCounter = ((intCounter & 0x00ff00ff00ff00ff) <<  8) | ((intCounter & 0xff00ff00ff00ff00) >>  8);
};

Credit: I found the solution in this GitHub Gist.