clear cart before payment

[Prabalpsingh7115]

Overview

1. This PR fixes or fixes part of #[fill_in_number_here].
2. This PR does the following: [Explain here what your PR does and why]

Essential Checklist

• [ ] The PR title starts with "Fix #bugnum: ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• [ ] "Allow edits from maintainers" is checked. (See here for instructions on how to enable it.)
• [ ] The PR is made from a branch that's not called "main/master".

Proof that changes are correct

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