For configuring gmail settings in laravel,
MAIL_DRIVER=sendmail
MAIL_HOST=smtp.gmail.com
MAIL_PORT=587
MAIL_USERNAME=your_email_address@gmail.com
MAIL_PASSWORD=your_gmail_address_password
MAIL_FROM_ADDRESS=your_email_address@gmail.com
MAIL_FROM_NAME="YOUR_USER_NAME"
MAIL_ENCRYPTION=tls
Also update the following in mail.php
'pretend' => false,
    'stream' => [
        'ssl' => [
            'allow_self_signed' => true,
            'verify_peer' => false,
            'verify_peer_name' => false,
        ],
    ],
To test your configuration put this code on api.php
Route::get('/emailTest',function(){
    $emailData = [
        'from'      => 'admin_email@gmail.com',
        'email'     => 'user_email@gmail.com',
        'password'  => 'user_password',
    ];
    // "mails.toUser" : this is my email template in resources
    Mail::send('mails.toAdmin',['emailData' => $emailData],function($message) use ($emailData){
        $message->to($emailData['email'])
            ->from($emailData['from'])
            ->subject('New User Registration');
    });
});