Prevent submission with duplicate email

Fluent Form Unique Email Validation

/*
 * Unique email vaildation
 */
 
add_action('fluentform_before_insert_submission', function ( $insertData, $data,  $formId ) {
		
    if($formId->id != 100) {    // You can pass your form id here 
       return;
    }    

    // Email based check
    $isExist = wpFluent()->table('users')

        ->where('user_email', $data['email'])   // make sure your email input name attibute is - email
        ->first();

    if($isExist) {

        wp_send_json(['errors' => [

            'restricted' => [
               "Sorry! there are already an account registered with your email."
            ]

        ]], 422);
    } 
}, 10, 3 );