FF_unique_users_ip.php

//Restrict repeated submission by user per day based on IP

add_action('fluentform_before_insert_submission', function ( $insertData, $data,  $formId ) {
    if($formId != 6) {    // You can pass your form id here
        return;
    }

    // IP based check
    $last24Hours = date('Y-m-d H:i:s', time() - 24 * 60 * 60);
    $isExist = wpFluent()->table('fluentform_submissions')
        ->where('form_id', $formId)
        ->where('ip', $insertData['ip'])
        ->where('created_at', '>', date('Y-m-d').' 00:00:00')
        ->first();


    if($isExist) {
        wp_send_json(['errors' => [
            'restricted' => [
                'Sorry! You can not submit twice in a day. Try again tomorrow'
            ]
        ]], 422);
    }

}, 10, 3 );