Yii2 reCaptcha Widget Class Not Found - yii2

Question

So I'm trying to use the Yii2 reCaptcha widget: http://www.yiiframework.com/extension/yii2-recaptcha-widget/
However, when setting the validation rule for it
['reCaptcha'], \himiklab\yii2\recaptcha\ReCaptchaValidator::className(), 'secret' => Yii::$app->params['reCAPTCHA.secretKey']
I get the error Class 'himiklab\yii2\recaptcha\ReCaptchaValidator' not found. I'm quite new to Composer and Yii2, so I'm not sure what I'm missing.
composer.json
{
"autoload" : {
"psr-4" : {
"Gaiatools\\Yii\\" : "src"
}
},
"name" : "gaiatools/site",
"require" : {
"php" : ">=7.0",
"himiklab/yii2-recaptcha-widget" : "*"
}
}
vendor/composer/autoload_psr4.php
// autoload_psr4.php #generated by Composer
$vendorDir = dirname(dirname(__FILE__));
$baseDir = dirname($vendorDir);
return array(
'yii\\composer\\' => array($vendorDir . '/yiisoft/yii2-composer'),
'yii\\' => array($vendorDir . '/yiisoft/yii2'),
'himiklab\\yii2\\recaptcha\\' => array($vendorDir . '/himiklab/yii2-recaptcha-widget'),
'cebe\\markdown\\' => array($vendorDir . '/cebe/markdown'),
'Gaiatools\\Yii\\' => array($baseDir . '/src'),
);

Answer 1

Add this line to require section in project-directory/composer.json file
"himiklab/yii2-recaptcha-widget" : "*"
Then run in project directory command:
composer update

Answer 2

Run the following command in a terminal inside your project directory. It will be added automatically in composer.json file.
composer require --prefer-dist "himiklab/yii2-recaptcha-widget" "*"

Answer 3

Often you get the error of class not found when the file containing the class definition is not added in current code using namespaces.
Please ensure that you have added the required namespace in file where you are setting the validation rule with following code at the top of file
use himiklab\yii2\recaptcha
Hope this will solve your problem