Razorpay Integration for PHP App

I run a small, custom-built PHP web application that already collects order details. Now I need Razorpay added so customers can complete one-time payments in multiple currencies.

Scope and deliverables:
• Embed Razorpay Checkout on the existing confirmation page, passing amount, currency and customer data from my PHP back-end.
• Verify the payment signature server-side and store a basic summary—payment_id, order_id, amount, currency, status, timestamp—in my MySQL table.
• Return a clear success or failure message to the front-end for redirects.
• Prove the flow works in sandbox and again in live mode, showing at least two currencies processed successfully.
• Provide concise setup notes so I can swap keys or migrate later.
• User should be able to cancel the order and should be able to track the return.

The app uses plain PHP without a framework, so please stick to vanilla PHP or the official razorpay-php SDK. I did not host the website yet or I have not registered in Razorpay Site also. I need support in razorpay registration as well.