I am using a PayPal button that redirects to a checkout/payment confirmation page that has payment info, payment methods, etc.
However, it is not obvious if the payment is one time or recurring.
The user could click on the amount and see more details, but I was wondering if I could show the subscription info by default to avoid confusion.
The subscription info is also presented after the payment has been processed in the receipt which is informative, but not ideal.
PayPal's checkout is designed to be equally usable from a mobile device or small/pop-up minibrowser, so the space on the right in your screenshot isn't available cross-platform.
The details of what is being paid for are meant to be shown by your own site before, on the page and in the receipt after, and are also available via the drop-down as shown in your screenshot.
You can't expand it by default.