如何使用PayPal呈现智能支付按钮？

I’m a bit confused trying to follow PayPal’s documentation for implementing Smart Payment Buttons in an e-commerce website. I’m following this guide: https://developer.paypal.com/docs/commerce-platform/payment/create-checkout-button/

I’ve “on-boarded” a seller using the Connected Path URL approach, but you don’t get much information—mainly the “merchant ID” in PayPal of the seller.

The next step in PayPal’s guide is then selling, and goes on to describe how to sell using Smart Payment Buttons (https://developer.paypal.com/docs/commerce-platform/payment/create-checkout-button/) but this is why I get fuzzy. PayPal’s documentation says I need an access token.

1. I’ve used OAuth before and in my experience, access tokens are transient. How am I supposed to use a transient token in the generating of a checkout button in my shopping cart?
2. If I am supposed to use an access token to generate a checkout button, how do I obtain one in the first place? My cart page is going to server-side rendered, and invoked by a customer (and not the seller). So the seller isn’t present at all to authenticate the creation of a checkout button.

If someone has integrated PayPal in shopping cart software before, I’d appreciate your advise on this hurdle!