Expense - After merging expenses with invalid tax, Tax field shows wrong rate

[mitarachim]

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Version Number: 9.3.37-0
Reproducible in staging?: Yes
Reproducible in production?: N/A - new feature, doesn't exist in prod
If this was caught during regression testing, add the test name, ID and link from BrowserStack: #83587
Email or phone of affected tester (no customers): jsiodjsodjojis@gmail.com
Issue reported by: Applause Internal Team
Bug source: Exploratory - Significant User Experience Deterioration
Device used: Mac 26.2 / Chrome
App Component: Money Requests

Action Performed:

1. Go to staging.new.expensify.com
2. Create workspace A.
3. Enable Taxes in workspace settings > More features.
4. Create workspace B.
5. Enable Taxes in workspace settings > More features.
6. Go to workspace B settings > Taxes.
7. Edit Tax Rate 1 to different name and rate.
8. Go to workspace chat A.
9. Create an expense with 5% rate.
10. Go to workspace chat B.
11. Create an expense with the edited tax rate in Step 7.
12. Open the expense from Step 11.
13. Click More > Merge.
14. Select expense from workspace A > Continue.
15. On details page, select tax rate from workspace B and report from workspace A. Select any details for other field.
16. Click Continue and Merge expenses.
17. Open the merged expense.
18. Click Tax field.

Expected Result:

Tax field will display the invalid rate from workspace B.

Actual Result:

Tax field displays tax rate from workspace A, but Tax RHP shows the invalid rate as selected.

Workaround:

Unknown

Platforms:

• Android: App
• Android: mWeb Chrome
• iOS: App
• iOS: mWeb Safari
• iOS: mWeb Chrome
• Windows: Chrome
• MacOS: Chrome / Safari

Screenshots/Videos

Bug7101673_1773360494777.5.mp4

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Issue Owner

Current Issue Owner: @hoangzinh

[melvin-bot]

You have been assigned to this deploy blocker because you recently merged this PR: #83587

[melvin-bot]

💬 A slack conversation has been started in #expensify-open-source

[github-actions]

👋 Friendly reminder that deploy blockers are time-sensitive ⏱ issues! Check out the open `StagingDeployCash` deploy checklist to see the list of PRs included in this release, then work quickly to do one of the following:

1. Identify the pull request that introduced this issue and revert it.
2. Find someone who can quickly fix the issue.
3. Fix the issue yourself.

[OSBotify]

🔍 Investigation Summary

Classification: Frontend bug
Causing PR: #83587 - "[Merge] Merge tax rates v2" by @dominictb (High confidence)
Related Issues: None

Recommendation: REVERT

PR #83587 introduced the taxName field to store tax rate names when merging transactions. However, the implementation allows invalid tax rates to be stored and displayed. When merging expenses with a tax rate from workspace B into workspace A (where that tax rate does not exist), the transaction.taxName field stores the invalid tax name from workspace B and displays it incorrectly.

Labels: Removed DeployBlocker label. This is a frontend bug in the App repository, so only DeployBlockerCash should remain to block the App deploy.

📋 Detailed Analysis

Evidence

PR #83587 added support for merging tax rates between expenses. The PR introduced a new taxName field on the Transaction type to store the human-readable tax rate name during merge operations.

Verification

The bug affects the tax field display logic in MoneyRequestView.tsx. Line 594 shows:

const taxRateValue = transaction?.taxName ?? taxRateTitle ?? fallbackTaxRateTitle;

This prioritizes transaction.taxName (which can store invalid tax names from other workspaces) over taxRateTitle (which is calculated from the current policy).

The PR modified these key files:

• src/components/ReportActionItem/MoneyRequestView.tsx - Changed tax display logic
• src/libs/MergeTransactionUtils.ts - Added taxName to merge fields
• src/types/onyx/Transaction.ts - Added taxName field

Root Cause

When merging expenses:

1. User selects a tax rate from workspace B (e.g., "Custom Tax 10%")
2. User selects workspace A as the destination report
3. The merge flow stores the tax name from workspace B in transaction.taxName
4. Workspace A does not have that tax rate
5. MoneyRequestView displays transaction.taxName (the invalid rate from workspace B)
6. The actual tax code points to a valid rate in workspace A, creating a mismatch between display and selection

The PR did not properly validate that the selected tax rate exists in the destination workspace before storing the taxName field.