Install the dependencies...
cd vue-integration
npm install
...log in to the developer dashboard and get your client ID from your default application. Change const CLIENT_ID = 'your-client-id';
in src/components/CheckoutPayment.vue so CLIENT_ID matches your sandbox client ID...
If you need help setting up your developer dashboard or finding your client ID, follow the first step in the getting started documentation to get API credentials
...then start:
npm run dev
Navigate to localhost:5173. You should see the app running.
The JavaScript SDK is imported via paypal-js in src/components/Checkout.vue where we set up a div to hold the buttons. Style, payment method, and other options can be specified in paypal.Buttons()
For more details and configuration options look at paypal-js usasge and the PayPal JavaScript SDK Complete Reference