Thank you very much for your help.

I am using Yii2. I want to use a REST POST request to send a list of words to the server, the server will translate the words and send back their translation.

When I send the POST request, I get this message in the browser JavaScript console:
name "Bad Request"
message "Missing required parameters: words"
code 0
status 400
type "yiiwebBadRequestHttpException"

I am running PHP using this command: php yii serve.

JavaScript

window.onload = (event) => {
    document.querySelector("#translate").addEventListener("click", translate)
}

function translate() {
    const textarea = document.getElementById("words");
    const words = textarea.value.replace(/rn/g, "n").split("n");
    post('http://localhost:8080/index.php/rest-translation/translate', words)
}

async function post(url, words) {
    console.log(words)

    let options = {
        method: "POST",
        body: JSON.stringify({words: words})
    }

    const response = await fetch(url, options)
    if (response.ok) {
        response.json()
    }
}

This is the view:

<?php

use yiihelpersHtml;
use yiiwidgetsDetailView;
use yiiwidgetsActiveForm;
use appassetsTranslationAsset;

/** @var yiiwebView $this */
/** @var appmodelsBook $book */
/** @var appmodelsBookSection $section */

$this->title = $section->title;
$this->params['breadcrumbs'][] = ['label' => Yii::t('app', 'Section'), 'url' => ['book']];
$this->params['breadcrumbs'][] = $this->title;
yiiwebYiiAsset::register($this);
?>
<div class="translate-section">

    <h1><?= Html::encode($this->title) ?></h1>

    <?= DetailView::widget([
        'model' => $book,
        'attributes' => [
            'id',
            'name',
        ],
    ]) ?>
    <?= DetailView::widget([
        'model' => $section,
        'attributes' => [
            'title',
        ],
    ]) ?>
    <div>
        <?php $form = ActiveForm::begin(); ?>
        <table>
            <tr>
                <td><textarea id="words"></textarea></td>
                <td><textarea id="first-translation"></textarea></td>
                <td><textarea id="second-translation"></textarea></td>
            </tr>
        </table>
        <button id="translate" type="button">Translate</button>

        <div class="form-group">
            <?= Html::submitButton(Yii::t('app', 'Save'), ['class' => 'btn btn-success']) ?>
        </div>

        <?php ActiveForm::end(); ?>

    </div>
    <?php TranslationAsset::register($this) ?>
</div>

This is the REST controller:

<?php

namespace appcontrollers;

use appmodelsTranslation;
use yiirestActiveController;

class RestTranslationController extends ActiveController
{
    public $modelClass = 'appmodelsTranslation';

    public function actionTranslate($words)
    {
        return  Translation::translate($words);
    }

    public function behaviors()
    {
        $behaviors = parent::behaviors();

        // remove authentication filter
        $auth = $behaviors['authenticator'];
        unset($behaviors['authenticator']);

        // add CORS filter
        $behaviors['corsFilter'] = [
            'class' => yiifiltersCors::class,
        ];

        // re-add authentication filter
        $behaviors['authenticator'] = $auth;
        // avoid authentication on CORS-pre-flight requests (HTTP OPTIONS method)
        $behaviors['authenticator']['except'] = ['options'];

        return $behaviors;
    }
}

This is the model:

<?php

namespace appmodels;

use Yii;

/**
 * This is the model class for table "translation".
 *
 * @property int $id
 * @property int $sourceEntryId
 * @property string $languageId
 * @property string $typeId
 * @property int $translationEntryId
 */
class Translation extends yiidbActiveRecord
{
    /**
     * {@inheritdoc}
     */
    public static function tableName()
    {
        return 'translation';
    }

    /**
     * {@inheritdoc}
     */
    public function rules()
    {
        return [
            [['sourceEntryId', 'languageId', 'typeId', 'translationEntryId'], 'required'],
            [['sourceEntryId', 'translationEntryId'], 'integer'],
            [['languageId', 'typeId'], 'string', 'max' => 10],
        ];
    }

    /**
     * {@inheritdoc}
     */
    public function attributeLabels()
    {
        return [
            'id' => Yii::t('app', 'ID'),
            'sourceEntryId' => Yii::t('app', 'Source Entry ID'),
            'languageId' => Yii::t('app', 'Language ID'),
            'typeId' => Yii::t('app', 'Type ID'),
            'translationEntryId' => Yii::t('app', 'Translation Entry ID'),
        ];
    }

    public static function translate($words)
    {
        //<TO DO>:Find and return the translation.
    }

    /**
     * {@inheritdoc}
     * @return TranslationQuery the active query used by this AR class.
     */
    public static function find()
    {
        return new TranslationQuery(get_called_class());
    }
}

config/web.php

<?php

$params = require __DIR__ . '/params.php';
$db = require __DIR__ . '/db.php';

$config = [
    'id' => 'basic',
    'basePath' => dirname(__DIR__),
    'bootstrap' => ['log'],
    'aliases' => [
        '@bower' => '@vendor/bower-asset',
        '@npm'   => '@vendor/npm-asset',
    ],
    'components' => [
        'request' => [
            // !!! insert a secret key in the following (if it is empty) - this is required by cookie validation
            'cookieValidationKey' => 'xxxxxxxx',
            'parsers' => [
                'application/json' => 'yiiwebJsonParser',
            ]
        ],
        /*'response' => [
            'format' => yiiwebResponse::FORMAT_JSON,
            'charset' => 'UTF-8',
            // ...
        ],*/
        'cache' => [
            'class' => 'yiicachingFileCache',
        ],
        'user' => [
            'identityClass' => 'appmodelsUser',
            'enableAutoLogin' => true,
        ],
        'errorHandler' => [
            'errorAction' => 'site/error',
        ],
        'mailer' => [
            'class' => yiisymfonymailerMailer::class,
            'viewPath' => '@app/mail',
            // send all mails to a file by default.
            'useFileTransport' => true,
        ],
        'log' => [
            'traceLevel' => YII_DEBUG ? 3 : 0,
            'targets' => [
                [
                    'class' => 'yiilogFileTarget',
                    'levels' => ['error', 'warning'],
                ],
            ],
        ],
        'db' => $db,
        
        'urlManager' => [
            'enablePrettyUrl' => true,
            'showScriptName' => true,
            'enableStrictParsing' => false
        ]
    ],
    'params' => $params,
];

if (YII_ENV_DEV) {
    // configuration adjustments for 'dev' environment
    $config['bootstrap'][] = 'debug';
    $config['modules']['debug'] = [
        'class' => 'yiidebugModule',
        // uncomment the following to add your IP if you are not connecting from localhost.
        //'allowedIPs' => ['127.0.0.1', '::1'],
    ];

    $config['bootstrap'][] = 'gii';
    $config['modules']['gii'] = [
        'class' => 'yiigiiModule',
        // uncomment the following to add your IP if you are not connecting from localhost.
        //'allowedIPs' => ['127.0.0.1', '::1'],
    ];
}

return $config;

My environment:
PHP 8.1.2-1ubuntu2.14 (cli) (built: Aug 18 2023 11:41:11) (NTS)
Zend Engine v4.1.2
with Zend OPcache v8.1.2-1ubuntu2.14
with Xdebug v3.2.1
Yii2 (2.0.48.1)

Thank you very much for your help.

I googled for a solution, but I didn’t find a anything.