Paypal checkout using Smart Payment Buttons gives error

Using Paypal API V2, what they now call Paypal checkout.

When loading the javascript of the button (Smart Payment Buttons) an error occurs.

Error: Attempted to load sdk version 5.0.73 on page, but version unknown already loaded. To load this sdk alongside the existing version, please specify a different namespace in the script tag, eg , then use the paypal_sdk namespace in place of paypal in your code.

Then the system gives an error on the line that launches the rendering of the buttons.

window.paypal_sdk.Buttons().render(‘#paypal-button-container’);

It says that “paypal.Buttons is not a function”