XMLRPC Error

When I try the create invoice example i get the following errors:

Notice: Trying to get property ‘params’ of non-object in /var/www/html/wp-includes/IXR/class-IXR-client.php on line 155

Notice: Trying to access array offset on value of type null in /var/www/html/wp-includes/IXR/class-IXR-client.php on line 155

The example is on the documentation here:
https://wp-invoice.github.io/docs/api/#gsc.tab=0

I am attempting to use the XMLRPC to create an invoice. I modified it a little to get it to work from a test page:

<?php 

//include_once( '../class-IXR.php' );
//include_once( '../class-wp-http-ixr-client.php' );

//Load WordPress 
  include_once( '../wp-load.php' );
  include_once( '../wp-includes/class-IXR.php' );
  include_once( '../wp-includes/class-wp-http-ixr-client.php' );

$client = new WP_HTTP_IXR_Client( 'https://{SITE}/xmlrpc.php' );

$client->query('wp.invoice', array(
  $method = 'create_invoice',
  $credentials = array('xmlrpc-user', 'password'),
  $args = array(
      'subject'     => 'Test API Invoice',
      'description' => 'Invoice descriptive information.',
      'type'        => 'invoice',
      'user_data'   => array(
          'user_email' => '[email protected]',
          'first_name' => 'John',
          'last_name'  => 'Smith'
      ),
      'deposit'     => 15.99,
      'due_date'    => array(
          'month' => '09',
          'day'   => '10',
          'year'  => '2013'
      ),
      'currency'    => 'USD',
      'tax'         => 10.5,
      'tax_method'  => 'after_discount',
      'status'      => 'active',
      'discount'  => array(
          'name'   => 'Your Discount',
          'type'   => 'amount',
          'amount' => 1.20
      ),
      'items' => array(
          array(
              'name' => 'Test item 1',
              'description' => 'Item 1 description',
              'quantity' => 2,
              'price' => 2.65,
              'tax_rate' => 1 //global 'tax' will be used in order to priority
          ),
          array(
              'name' => 'Test item 2',
              'description' => 'Item 2 description',
              'quantity' => 4,
              'price' => 3.85
          )
      ),
      'charges' => array(
          array(
              'name' => 'Fee 1',
              'amount' => 0.56
          ),
          array(
              'name' => 'Fee 2',
              'amount' => 0.99,
              'tax' => 15 //global 'tax' will be used in order to priority
          )
      )
  )
));

$new_invoice = $client->getResponse();
?>