I am trying to integrate paypal api with PHP compared to the old button form that I have used to date on my sites. But there is one thing that is not clear to me, is it more correct to integrate paypal with client_id and secret or through the codes provided in the account panel (api username, api password and signature)? I followed the REST API integration guide (version 2) but they require client_id and secret. So what is the data in the account panel for? Anyone can clarify my ideas? Thank you
The API username, password, and signature is used by the classic NVP/SOAP APIs, which are much older than the REST API. They exist only for backwards compatibility with old shopping cart software and such integrations.
The v2/checkout/orders API should be used for current PayPal Checkout integrations. Pair two routes on your server (one for create order, one for capture order) that return/output only JSON data (never any HTML or text) with this JS approval flow.