Fix net_amount double-deducting GST on Razorpay gateway fees

[TheShahnawaaz]

Root Cause

Razorpay's payment API returns two fields in the payment object:

• fee — the total amount deducted from settlement, which is base_fee + GST (all-in)
• tax — the GST portion only, which is already contained within fee

The previous code treated tax as an additional deduction on top of fee:

// Before — GST counted twice
net_amount = amount - fee - tax

// After — correct
net_amount = amount - fee

This meant every confirmed payment stored a net_amount that was understated by exactly the tax value (22 paise per ₹60 payment). Every financial report showed a lower "Net received" than what Razorpay actually settled.

Example (29-payment trip):

	Amount
Gross collected	₹1,740.00
Razorpay deduction (fee)	₹41.18
Razorpay settled (correct)	₹1,698.82
Previously reported net	₹1,692.44
Discrepancy	₹6.38 (= total GST across 29 payments)

Changes

backend/src/services/payment/payment.service.ts

Fixed net_amount calculation in all three code paths:

• Payment verification flow (frontend-initiated)
• Webhook handler: pending → confirmed
• Webhook handler: already confirmed (fill-in update)

backend/migrations/021_create_reports_module.sql

• report_financials view: fixed the NULL fallback formula from amount - (fee + tax) / 100 to amount - fee / 100
• reports_summary view: fixed total_gateway_deductions from SUM(gateway_fees + gateway_tax) to SUM(gateway_fees) — was double-counting GST in the summary

backend/migrations/014_add_payment_fee_columns.sql

Corrected the net_amount column comment from amount - fee - tax to amount - fee so future developers don't reintroduce the same bug.

frontend/src/pages/admin/reports/ReportDetailPage.tsx

Fixed the "Gateway fees" display line from gateway_fees + gateway_tax to gateway_fees only, making the on-screen breakdown self-consistent:

Online Payments    ₹1,740.00
Gateway fees         -₹41.18   ← actual Razorpay deduction
Net received       ₹1,698.82   ← matches Razorpay dashboard

Notes

• Historical payment records are intentionally left unchanged
• gateway_tax column is still stored for GST accounting/tax records — it is just no longer subtracted from net_amount
• On a fresh database with all migrations applied, all calculations will be correct from the first transaction

[vercel]

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Project	Deployment	Actions	Updated (UTC)
cab-management-system	Ready	Preview, Comment	May 2, 2026 4:33pm
cab-management-system-b59a	Ready	Preview, Comment	May 2, 2026 4:33pm

[Copilot]

Pull request overview

Fixes incorrect “net received” calculations by removing a double-deduction of GST (tax) on Razorpay gateway fees across backend payment flows, reporting SQL views, and the admin report UI—aligning stored/reporting values with Razorpay settlements.

Changes:

• Backend: compute net_amount as amount - fee (since Razorpay fee already includes GST) in verification + webhook paths.
• SQL: update report_financials and reports_summary views to stop subtracting/aggregating gateway_tax on top of gateway_fee.
• Frontend: display “Gateway fees” as gateway_fees only (no longer gateway_fees + gateway_tax).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
frontend/src/pages/admin/reports/ReportDetailPage.tsx	Updates gateway fees line item to match the corrected definition of deductions (avoid adding GST twice).
backend/src/services/payment/payment.service.ts	Fixes net_amount calculation in verify + webhook flows to avoid double-deducting GST.
backend/migrations/021_create_reports_module.sql	Fixes report views’ fallback and summary aggregations to avoid double-counting GST in deductions/net revenue.
backend/migrations/014_add_payment_fee_columns.sql	Updates net_amount column documentation to reflect the corrected calculation.