Improve payment method

[beytullahdanis]

This pull request introduces improvements to the paymentSuccess method, making the code more readable and modular. Changes include:

• Utilizing isEmpty() for cart check.
• Extracting logic into separate methods for better readability.
• Creating helper methods for transaction addition and notification.
• Elimination of redundant break; statements.
• Simplification of conditional checks within the loop for better readability.
• Reduction of unnecessary if else blocks.