FluentForms - Email Blacklist - Specific Forms

functions.php

<?php

// FluentForms - Email Blacklist - Specific Forms
// Need help: https://bloggerpilot.com/snippet-fluentforms-e-mail-blacklist/

add_filter('fluentform_validate_input_item_input_email', function ($error, $field, $formData, $fields, $form) {

  The ID(s) of the form
  $targetFormId = [13,14];

  // These listed domains will fail to submit the form
  $blacklistDomains = ['gmail.com', 'hotmail.com', 'test.com'];
  
  // You can edit your error message here
  $errorMessage = 'The provided email domain is not accepted';
  
  if (!in_array($form->id, $targetFormId)) {
    return $error;
  }

  $fieldName = $field['name'];

  if (empty($formData[$fieldName])) {
    return $error;
  }

  $valueArray = explode('@', $formData[$fieldName]);
  $inputDomain = array_pop($valueArray);

  if (in_array($inputDomain, $blacklistDomains)) {
    return [$errorMessage];
  }
  
  return $error;
}, 10, 5);