Create Paystack Account
Copy Your API Test Key
Our Paystack Class
Initialize_Transaction() Method Explained
Parameters needed to initialize transaction
Headers
Authorization and Content-Type
Body Param
Amount and Email
Optional Parameters
Execute_Transaction() Method
Authorize_Payment() Method Explained
The Mainline
Call Initialize_Transaction Method
Call Execute_Transaction()
Close curl object
Call Authorize_Payment()
Put the mainline code together
What’s Next
Callback URL Processing
Callback URL Explained

See complete tutorial here https://firstclicklimited.com/tutorials/index.php/2021/01/30/how-to-integrate-paystack-to-receive-payment-implemented-in-php/