Form Validation Prompt after .api response - Semantic Ui

Question

i'm using semantic-ui form validation in my code. I'm sending a data to server for checking if is has the same value-or not. if server value has same with my sending data, writing a message, i want to show that message into form validation prompt are. But how! Please give me a hand about this. Here is my code:

<form class="ui form segment">
     <div class="field">
         <label>Email</label>
            <input type="email" name="email" id="email">
      </div>
      <div class="ui submit button">Validate Email</div>
      <div class="ui error message"></div>
</form>

<script>
      $('.ui.form')
          .form({
              on: 'blur',
              fields: {
                  email: {
                      identifier  : 'email',
                      rules: [{type: 'email', prompt: 'This is not a valid email adress.'}]
                      }
                  },
            
                    onSuccess: function() {
                        return false; // false is required for dont let submit the form, (prevent refreshing)
                    } 
         })
                .api({        
                    url     : 'register.php',
                    method  : 'POST',
                    serializeForm: true,
                    onResponse: function(response) {
                            if(response == 0){
                        console.log('You are eligible, you can join us');
                            }else{
                        console.log('Your email already in our database, try another one');
                            }    
                        }
                });
</script>

Here is my register php;

if(isset($_POST['email'])){

    $q="SELECT * FROM users WHERE email = '$_POST[email]'";
    $r = mysqli_query($dbc, $q);
    
    $response = mysqli_num_rows($r);

        echo $response;
}

As you can see, i'm consoling results from server. I want to prompt this message to form validation prompt, like 'This is not a valid email adress.'.

Thanks already.