You must have the latest version of the Robot Ninja Helper plugin which tells Robot Ninja what PayPal Advanced Layout you have chosen in gateway settings in WooCommerce > Settings > Payments.
PayPal Advanced Layouts
The PayPal Advanced gateway plugin comes with multiple options to choose which PayPal layout you'd like to send your customers to.
Layout A & B take the customer off-site to PayPal to complete the payment and then are redirected back to your store on payment completion. Layout C takes the customer to a separate Pay for Order page within your store however the payment form is within a hosted PayPal iFrame.
All of these layouts are supported by Robot Ninja.