Issue with multiple percentage discounts

[serhiikv]

Preconditions and environment

• Magento 2

Steps to reproduce

1. Create new cart price rules with the following configuration

Rule 1:

Rule Name: 10% Fix Discount
Coupon: No Coupon
Conditions: Apply for all product
Action: 
    Apply: Percent of product price discount
    Discount Amount: 10

Rule 2:

Rule Name: 3% Fix Discount
Coupon: No Coupon
Conditions: Apply for all product
Action: 
    Apply: Percent of product price discount
    Discount Amount: 3

2. Order product with price = $12
3. Query REST endpoint orders/{id} for this order

Expected result

In API response receive discount_percent equals 12.7

Actual result

In API response receive discount_percent equals 13

Additional information

Magento2 REST api for orders has one field for discount_percent. In case when order has multiple discounts they are just added. This results in incorrect calculation.

e.g.
order amount 12. discount1 = 10%, discount2 = 3%.
How magento2 does calculation:

12 - (12 * 0.1) = 10.8 // calculate 10%
10.8 - (10.8 * 0.03) = 10.476 // next calculate 3%
12 - 10.476 = 1.524 // total discount

But if API response is used to calculate discount - it will result in wrong discount amount:

12 - (12 * 0.13) = 10.44 // calculate 13% provided by API field `discount_percent`
12 - 10.44 = 1.56 // total discount is different

The correct discount_percent in this case would be 12.7:

12 - (12 * 0.127) = 10.476 
12 - 10.476 = 1.524 // correct discount amount

Is it possible to change logic behind discount_percent field in REST API response in case of multiple discounts?

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

Hi @engcom-Bravo. Thank you for working on this issue.
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[engcom-Bravo]

@magento give me 2.4-develop instance

[magento-deployment-service]

Hi @engcom-Bravo. Thank you for your request. I'm working on Magento instance for you.

[magento-deployment-service]

Hi @engcom-Bravo, here is your Magento Instance: https://16d879d04480f916c2d2f786540d1680.instances-prod.magento-community.engineering
Admin access: https://16d879d04480f916c2d2f786540d1680.instances-prod.magento-community.engineering/admin_38e1
Login: 765294e7
Password: 49ec4bb9a057

[engcom-Bravo]

Hi @serhiikv,

Thanks for your reporting and collaboration.

We have verified the issue in Latest 2.4-develop instance and the issue is reproducible.Kindly refer the screenshots.

In API response receive discount_percent equals 13

Hence Confirming the issue.

Thanks.