Craft CMS 3 error in Windows installation process I was tried to run Craft 3 on a Windows machine, it has shown the multiple errors.

An Error occurred while handling another error:
yii\base\InvalidConfigException: craft\web\Request::cookieValidationKey must be configured with a secret key. in D:\xampp\htdocs\craft\vendor\yiisoft\yii2\web\Request.php:1554
Stack trace:
#0 D:\xampp\htdocs\craft\vendor\yiisoft\yii2\web\Request.php(1536): yii\web\Request-&gt;loadCookies()
You'll get that error (regardless of OS) if the SECURITY_KEY variable isn't set in your .env file: https://github.com/craftcms/craft/blob/master/.env.example#L5

See this step in the install docs: https://docs.craftcms.com/v3/installation.html#step-3-set-a-security-key

If you run the craft setup terminal command, it will generate that key for you, but depending on how you install Craft, you can also manually set it.