Rederecting to php file after recaptcha I'm not a robot checkbox not checked?

Question

When I put this upon the website, it's always rederecting to the php file, I get a blank page. Why is that? An idea how to fix it? this is the code: html

Ime / Naziv tvrtke:


Telefon:

            <label for="email"> E-mail:  </label><br>
            <input type="text" id="email" name="email" required><br><br>

            <label for="predmet"> Predmet:  </label><br>
            <input type="text" id="predmet" name="predmet"><br><br>

            <div class="g-recaptcha" data-sitekey="xxxx"></div>

            <label for="poruka"> Poruka/Upit:  </label><br>
            <textarea name="poruka" rows = "6" cols="25" required></textarea><br><br>

            <input type="submit" value="Podnesi"><input type="reset" value="Obriši">
        </form>

php:

success){ mail($recipient, $subject, $formcontent, $mailheader); echo 'alert("Success in Google reCAPTACHA")'; } else { echo 'alert("Error in Google reCAPTACHA")'; } }else{ echo "error!!!"; } } ?>