How should a travel booking engine adapt its checkout to the updated UPI limits for travel-related payments?pil

You must work with your bank for merchant verification and interface with a payment gateway that supports the most recent UPI APIs in order to demonstrate real-time eligibility for larger UPI limits.  The higher limit choice can then be dynamically displayed at your e-commerce checkout for purchases in qualified categories like travel, investments, or insurance.

When QA tests UPI refunds and reversals under the new high-limit rules, they should focus on four main buckets: correctness, compliance, concurrency, and reconciliation.
Core refund/reversal validations

• Full refund success – Initiate a refund equal to the original transaction amount (even if >₹2L) and verify it posts successfully for verified merchants.
• Partial refund success – Validate that multiple partial refunds against the same UPI Ref ID are allowed and reconcile correctly.
• Refund cap breach – Try refunding more than the original amount or beyond daily refund limits to ensure proper error (LIMIT_EXCEEDED or PSP-defined).
• Reversal after auto-refund – Simulate double credit scenarios where your system mistakenly retries a refund and confirm idempotency prevents duplicates.

Timing and window edge cases

• Refund outside allowed window – Test refunds initiated after NPCI’s refund cut-off (typically T+1/T+2) to confirm they’re rejected gracefully.
• High-value reversal delay – Validate how long large reversals take to reflect in settlement files; your ERP should still mark them “pending reversal” until confirmation.
• Refund retry under PSP timeout – Simulate PSP latency during peak hours to verify your retry/backoff logic (especially for ₹5L+ refunds).

Concurrency and split-payment scenarios

• Split invoice refund – If the original payment was split into multiple UPI legs, ensure refund logic correctly targets each UPI Ref ID and matches proportionally.
• Concurrent refunds – Two refund requests fired at once for the same transaction should trigger one success and one duplicate rejection.
• Daily limit overlap – Simulate when a merchant is close to their ₹10L daily limit and issues a refund that would push them past it — should fail or queue per PSP policy.

Reconciliation and ledger checks

• Refund reflected in PSP file – Make sure every refund entry appears in NPCI or PSP settlement files and matches your ledger.
• Customer advance vs. revenue correction – Test accounting mappings: refund on advance should reverse liability, refund on sale should reverse revenue.
• Mismatch alerting – Simulate a failed refund that PSP reports as success (or vice versa) and ensure your reconciliation job flags the mismatch automatically.

Gather the constraints up front

• Source per-transaction and per-day caps from your PSP / acquirer (or from a config table you keep updated per NPCI rules + merchant verification status + MCC).
• Also fetch merchant’s remaining daily allowance (from PSP API or your local ledger of successful UPI receipts).
• Enforce any PSP-specific rules (min txn amount, max legs allowed, supported UPI modes).

Decide UX / business rules

• Decide whether splitting is automatic (ERP will try to split) or opt-in (customer chooses split/pay later).
• Prefer showing the user: total, per-leg amounts, number of legs, and which payment methods are alternatives (card/netbanking) before attempting collects.
• For B2B invoices, ask if partial payments are allowed; if not, block UPI and suggest alternate flows.

Algorithm to compute safe splits (basic, robust)

• Let Tcap = per-transaction cap, Dcap = daily cap, R = remaining daily allowance for merchant, Amount = invoice total.
• Effective single-leg ceiling Ceil = min(Tcap, R).
• If Amount <= Ceil → single collect.
• Else compute legs greedily: take as many Ceil legs as needed, last leg = remainder. If last leg < PSP minimum amount, adjust by balancing (e.g., distribute across legs to keep all ≥ min).
• Also check maximum number of legs allowed; if exceeded, fallback to alternate payment or require manual handling.

Orchestration & atomicity (critical)

• •    Create a single InvoicePaymentPlan record linked to invoice with legs array (leg_id, amount, status, psp_txn_id, upi_ref).
• For each leg call PSP pre-check API (if available) to confirm remaining daily limit and allowed amount. If no pre-check, proceed but be prepared to handle failures.
• Execute collects sequentially or in controlled parallelism: prefer sequential (leg1 → leg2 → …) because daily allowances and race conditions can cause mid-flow failures.
• Implement reversible flows via PSP APIs (reversals/refunds) and mark everything in your ledger before returning success to caller.

Idempotency & retries

• Use idempotency keys per leg (invoiceId:legIndex:attemptId) so retries don’t double-charge.
• Backoff / retry on transient errors; on definitive errors (LIMIT_EXCEEDED, DAILY_LIMIT_REACHED) stop retries and surface next steps to user.

Reconciliation & GST / e-invoice mapping

• Store psp_txn_id and upi_ref for every leg and include them in your GST e-invoice Payment array (one entry per leg).
• Ensure your settlement batch logic aggregates legs correctly: settlement files from PSP may show separate credits — map them to invoice via psp_txn_id.
• If auto-reversal happens, generate credit note / adjusted invoice and record reversal UPI ref.

Notifications & UX

• Notify user/customer at three touchpoints: (a) when split is created, (b) as each leg succeeds/fails, (c) final invoice status.
• Provide clear error messages: UPI daily cap reached — try smaller amount, card, or complete tomorrow.

Auditability & monitoring

• Log every API request/response and store raw PSP error codes (to tune thresholds).
• Add alerts for patterns: many LIMIT_EXCEEDED responses, high rate of compensations, reconciliation mismatches.
• Track KPIs: split success rate, average legs per invoice, compensation rate, reconciliation delta, time-to-full-payment.

Edge cases & testing

• Simulate concurrent spends that consume merchant’s remaining allowance mid-flow (race conditions). Build tests that:
• Force second-leg DAILY_LIMIT_REACHED and ensure compensation works.
• Simulate webhook/callback lost and verify polling reconciles status.
• Verify idempotency under duplicate webhooks or client retries.
• Test refunds across split legs: full refund should create refunds across legs proportionally or in defined order (document policy).

Security, compliance

• Don’t store PAN/card data — store only PSP tokens and UPI refs. Ensure logs containing sensitive identifiers are redacted.
• Maintain audit trail for NPCI/RBI compliance — per-txn UPI refs, timestamps, merchant verification status, and settlement files.

Implementation sketch (pseudo-code)
def split_invoice(invoice)

Rollout & Ops

• Roll out with a canary: only for verified merchants and a small % of invoices.
• Feature flag the auto-split behavior so you can disable instantly.
• Provide support playbooks for agents to handle partial payments and reconciliation questions.

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