Cart Price rule discounts incorrect value when shipping is included and an item in the cart is non-taxable

[techsteamdesk]

Preconditions and environment

1. Magento Open Source 2.4.6-p8 without sample data is installed.
2. No custom modules or theme customisation
3. Default Luma theme
4. Set up tax rules and tax rates and zones with a tax rate of 20% for all UK Addresses.
5. Set up the sales > tax configuration as per the attached screenshot. Note that there are no warnings of tax rounding errors.
6. Create a some new products. Create two simple products one that is taxable and one that is not. Create a configurable product with taxable and non-taxable child products. Add all the products to a test category.
7. Set up and enable the flat rate shipping method for £4.80.
8. Create a Cart Price rule that applies a fixed value to the whole cart up to £60 and has the ‘Apply to Shipping Amount’ setting set to yes. See attached screenshot for details.

Steps to reproduce

1. Navigate to storefront as a guest.
2. Open Test Category.
3. Click "Add to Cart" on a Product that is not taxable.
4. Open mini shopping cart and click "View and edit cart".
5. Change the quantity in cart so that it exceeds the £60 coupon discount.
6. Apply the previously configured coupon code.

Expected result

Order is discounted by £60

Actual result

Order is discounted by a different amount.

Additional information

If you change the product in the cart to one that is taxable with otherwise identical conditions the Order is correctly discounted by £60:

However any combination of products in the cart that include a tax free product causes the discount to be incorrect:

Release note

No response

Triage and priority

• Severity: S0 - Affects critical data or functionality and leaves users without workaround.
• Severity: S1 - Affects critical data or functionality and forces users to employ a workaround.
• Severity: S2 - Affects non-critical data or functionality and forces users to employ a workaround.
• Severity: S3 - Affects non-critical data or functionality and does not force users to employ a workaround.
• Severity: S4 - Affects aesthetics, professional look and feel, “quality” or “usability”.

[m2-assistant]

Hi @techsteamdesk. Thank you for your report.
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[m2-assistant]

Hi @engcom-Bravo. Thank you for working on this issue.
In order to make sure that issue has enough information and ready for development, please read and check the following instruction: 👇

• 1. Verify that issue has all the required information. (Preconditions, Steps to reproduce, Expected result, Actual result).
• 2. Verify that issue has a meaningful description and provides enough information to reproduce the issue.
• 3. Add Area: XXXXX label to the ticket, indicating the functional areas it may be related to.
• 4. Verify that the issue is reproducible on 2.4-develop branch
  Details

  - If the issue is reproducible on 2.4-develop branch, please, add the label Reproduced on 2.4.x.
  - If the issue is not reproducible, add your comment that issue is not reproducible and close the issue and stop verification process here!
• 5. Add label Issue: Confirmed once verification is complete.
• 6. Make sure that automatic system confirms that report has been added to the backlog.

[m2-assistant]

Hi @engcom-Delta. Thank you for working on this issue.
In order to make sure that issue has enough information and ready for development, please read and check the following instruction: 👇

• 1. Verify that issue has all the required information. (Preconditions, Steps to reproduce, Expected result, Actual result).
• 2. Verify that issue has a meaningful description and provides enough information to reproduce the issue.
• 3. Add Area: XXXXX label to the ticket, indicating the functional areas it may be related to.
• 4. Verify that the issue is reproducible on 2.4-develop branch
  Details

  - If the issue is reproducible on 2.4-develop branch, please, add the label Reproduced on 2.4.x.
  - If the issue is not reproducible, add your comment that issue is not reproducible and close the issue and stop verification process here!
• 5. Add label Issue: Confirmed once verification is complete.
• 6. Make sure that automatic system confirms that report has been added to the backlog.

[engcom-Delta]

Hi @techsteamdesk ,

Thanks for your reporting and collaboration.
We have re-verified the issue in latest 2.4-develop instance and the issue is reproducible.
Kindly refer the screenshots.

Steps to reproduce :

1. Navigate to storefront as a guest.
2. Open Test Category.
3. Click "Add to Cart" on a Product that is not taxable.
4. Open mini shopping cart and click "View and edit cart".
5. Change the quantity in cart so that it exceeds the £60 coupon discount.
6. Apply the previously configured coupon code.

Observe Cart Price rule discounts incorrect value when shipping is included and an item in the cart is non-taxable.

Thanks.