fluentform_reoon_email_validation.php

add_action('fluentform_before_insert_submission', 'validate_email_reoon', 10, 3);

function validate_email_reoon($insertData, $data, $form)
{
   if($form->id != 633) { //change the form id with your form id
      return;
   }
	
	$apiKey = 'lYlSwj3Uxt5iGecFTHYdqKC4xBQYaClf'; //put your api key here
	
	$apiUrl = 'https://emailverifier.reoon.com/api/v1/verify?email='.$data['email'].'&key='.$apiKey.'&mode=quick';
	
	$response = wp_remote_get($apiUrl);

	
	$body = json_decode($response['body']);
	
	if($body->status != 'valid'){
		return wp_send_json_error("This is not a valid email");
	}

   // DO your stuffs here
}