[Awaiting checklist completion] [$250] Expense - Splitting a Per Diem Expense with Large Amount Causes Unexpected Error

[jponikarchuk]

If you haven’t already, check out our contributing guidelines for onboarding and email contributors@expensify.com to request to join our Slack channel!

---

Version Number: V9.2.46-0
Reproducible in staging?: Yes
Reproducible in production?: Yes
If this was caught during regression testing, add the test name, ID and link from BrowserStack: https://test-management.browserstack.com/projects/2219752/test-runs/TR-1856/folder/13176670/45748766/999689654
Email or phone of affected tester (no customers): Slottwo1 72old.approver@gmail.com
Issue reported by: Applause Internal Team
Device used: Redminote 10s android 13
App Component: Money Requests

Action Performed:

1. Go to https://staging.new.expensify.com/home
2. Open workpace settings
3. Enable per diem feature and import per diem rates
4. Create a per diem expense
   Algeria - overnight - 999999999999
5. Complete the flow
6. Note user can create per diem expense with big amount without error
7. Tap more - Split expense
8. Tap save

Expected Result:

If the system allows creation of a Per Diem expense with a large amount, it should also allow splitting that expense without any error.

Actual Result:

*User is able to create a Per Diem expense with a very large amount (e.g., 999999999999) without any error.

*However, when attempting to split the same expense and tapping Save, an unexpected error occurs.

Workaround:

Unknown

Platforms:

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

Screenshots/Videos

1.mp4

View all open jobs on GitHub

Upwork Automation - Do Not Edit

• Upwork Job URL: https://www.upwork.com/jobs/~021986766496225604344
• Upwork Job ID: 1986766496225604344
• Last Price Increase: 2025-11-14

Issue Owner

Current Issue Owner: @hoangzinh

[melvin-bot]

Triggered auto assignment to @twisterdotcom (Bug), see https://stackoverflow.com/c/expensify/questions/14418 for more details. Please add this bug to a GH project, as outlined in the SO.

[mukhrr]

@twisterdotcom so user shouldn't create per diem report with large amount before any action?!
Or at least, we have to validate when saving split expense?

[mukhrr]

🚨 Edited by proposal-police: This proposal was edited at 2025-11-08 11:21:00 UTC.

Proposal

Please re-state the problem that we are trying to solve in this issue.

Users can create Per Diem expenses with extremely large amounts (e.g., 999999999999 cents) without any validation error. However, when they attempt to split these expenses, the system throws an unexpected error instead of allowing the split operation or showing a clear validation message.

What is the root cause of that problem?

Saving per diem only validates if we have subrates and missing validation for max amount

App/src/components/MoneyRequestConfirmationList.tsx

Lines 905 to 908 in 2087489

	if (isPerDiemRequest && (transaction.comment?.customUnit?.subRates ?? []).length === 0) {
	setFormError('iou.error.invalidSubrateLength');
	return;
	}

And also onSaveSplitExpense() function in SplitExpensePage.tsx doesn't validate that the transaction amount is within safe limits before attempting to split it

What changes do you think we should make in order to solve the problem?

We already have validateAmount func to validate max amount.

App/src/libs/MoneyRequestUtils.ts

Lines 44 to 54 in 2087489

	function validateAmount(amount: string, decimals: number, amountMaxLength: number = CONST.IOU.AMOUNT_MAX_LENGTH, shouldAllowNegative = false): boolean {
	const regexString =
	decimals === 0
	? `^${shouldAllowNegative ? '-?' : ''}\\d{1,${amountMaxLength}}$` // Don't allow decimal point if decimals === 0
	: `^${shouldAllowNegative ? '-?' : ''}\\d{1,${amountMaxLength}}(\\.\\d{0,${decimals}})?$`; // Allow the decimal point and the desired number of digits after the point
	const decimalNumberRegex = new RegExp(regexString, 'i');
	if (shouldAllowNegative) {
	return amount === '' || amount === '-' || decimalNumberRegex.test(amount);
	}
	return amount === '' || decimalNumberRegex.test(amount);
	}

We can validate per diem expense creation in src/components/MoneyRequestConfirmationList.tsx:

    const confirm = useCallback(
        (paymentMethod: PaymentMethodType | undefined) => {
            if (!!routeError || !transactionID) {
                return;
            }
    // existing logic ...

                 if (isPerDiemRequest) {
                    const perDiemAmountInCents = computePerDiemExpenseAmount(transaction.comment?.customUnit ?? {});
                    const perDiemAmountString = convertToFrontendAmountAsString(perDiemAmountInCents, iouCurrencyCode);
                    if (!validateAmount(perDiemAmountString, decimals)) {
                        setFormError('iou.error.invalidAmount');
                        return;
                    }
                }
    // existing logic ...

We calculate per diem rates amount by multiplying the subrate amount and the unit rate as mentioned here #74550 (comment) via computePerDiemExpenseAmount

https://github.com/Expensify/App/blob/25c7f6e93f1d2d32c8175a87a51e83996e4df881/src/libs/actions/IOU.ts#L3690C1-L3693C2

Optionally, we can validate splitting it in src/pages/iou/SplitExpensePage.tsx

    const currencyDecimals = getCurrencyDecimals(transactionDetails.currency);

    const onSaveSplitExpense = useCallback(() => {
            if(validateAmount(String(transactionDetailsAmount), currencyDecimals)) {
                setErrorMessage(translate('common.error.invalidAmount'));
                return;
            }
    // existing logic ...

What alternative solutions did you explore? (Optional)

We may not need to validate split expense as there is no need for that if we validate when creating (can be discussed)

result:

In my case, per diem rate was 23000 and max quantity I could enter is 43478

result_74550.mp4

[melvin-bot]

Job added to Upwork: https://www.upwork.com/jobs/~021986766496225604344

[melvin-bot]

Triggered auto assignment to Contributor-plus team member for initial proposal review - @hoangzinh (External)

[FitseTLT]

@twisterdotcom Don't you think an internal engineer (familiar with perdiem feature) check if this should be fixed from BE because it looks illogical to work for the creation of the expense but fail on the split as the amount would be half the original amount.

[twisterdotcom]

Hmm well yes, I do think we shouldn't be able to create any expenses greater than IOU.AMOUNT_MAX_LENGTH. Do we think this should be internal then?

[mukhrr]

updated proposal