I’m adding PayPal Checkout to my existing PHP site so users can pay each time they call one of two API-driven services. Here’s what I need: • Implement PayPal Checkout for One-time Payments, displaying the appropriate price for either service. • Build the PHP server-side flow (using the official PayPal SDK or REST endpoints) to create, capture, and verify each transaction. • Configure and demonstrate Sandbox mode first, then provide clear steps and code changes for switching to Live credentials. • Return the PayPal response to my app, update my database with the transaction status, and trigger the API call only after successful payment. • Supply concise setup notes so I can maintain client IDs, secrets, and webhook URLs securely. The existing site runs on standard LAMP hosting; no framework dependency is required, but clean, well-commented PHP is essential. If you have prior PayPal Checkout experience and can walk me through a short test round in Sandbox, let’s get started right away.