Payment stack audit
Understand the current state of your payment infrastructure with Cardflo's Payment Stack Audit. We provide an objective assessment of your existing systems, identifying areas for optimisation, cost reduction, and enhanced performance.
This audit establishes a clear baseline for future strategic payment decisions.
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The overview
A payment stack audit involves a systematic review of the technical and financial layers within a merchant's transaction lifecycle. This process examines the integration between the gateway, the merchant identification (MID) structure, and the downstream acquirers to identify latency, redundancy, or technical fragility.
Beyond the basic connectivity, the audit assesses the logic governing routing, 3D Secure (3DS) implementation, and fraud filter sensitivity.
By reviewing historical transaction data and decline reason codes, an organisation can determine whether failures stem from technical integration issues, issuer-side risk appetites, or regional compliance hurdles.
The audit functions at the intersection of treasury, engineering, and compliance, ensuring that scheme rules are met while minimising the total cost of acceptance.
This review provides a concrete map of the current architecture, highlighting where fragmentation in the stack leads to inefficient settlement cycles or excessive scheme fees that erode margins in high-volume environments.
How it works
Gateway and Acquirer Mapping
The auditing process begins by documenting every connection point between the checkout interface and the final settlement account. This includes identifying all active gateways, primary and backup acquirers, and any third-party processors.
Consultants verify if the current geographic footprint of acquirers aligns with the merchant's actual customer base to reduce cross-border fees.
Data and Error Analysis
Auditors extract raw transaction logs to analyse the ratio of hard declines to soft declines. By categorising refusal reasons, such as insufficient funds versus suspected fraud or technical timeouts, patterns emerge regarding the health of the integration.
This step pinpointing where valid transactions are being incorrectly blocked by aggressive risk settings.
Commercial and Fee Review
A granular review of the fee structure is conducted, typically focusing on interchange levels, scheme fees, and any blended pricing markups.
The audit checks for consistency between the agreed Merchant Service Charge (MSC) and the actual debits from settlement files, ensuring that the merchant is not overpaying for non-qualified transactions.
Compliance and Security Assessment
The audit evaluates the implementation of Strong Customer Authentication (SCA) under PSD2 and the current status of PCI DSS compliance.
This includes reviewing how payment card data is vaulted and whether the merchant utilises network tokens to maintain security whilst reducing the risk of data breaches or non-compliance penalties.
Reporting and Strategy Formulation
Findings are synthesised into a technical roadmap that prioritises remediation efforts based on potential impact. This includes suggesting adjustments to retry logic, proposing the consolidation of redundant MIDs, or recommending specific acquirers that demonstrate higher authorisation rates for particular Merchant Category Codes (MCCs) or regions.
Why it matters
Reduction in Operational Overheads
Many businesses accumulate payment vendors due to expansion or legacy requirements, resulting in fragmented reporting and manual reconciliation processes. A payment stack audit identifies these redundancies, allowing teams to consolidate infrastructure.
This reduction in complexity lowers the administrative burden on finance departments and reduces the technical debt associated with maintaining multiple, often outdated, API integrations.
Authorisation Rate Optimisation
Small discrepancies in how data is passed to the issuer can lead to higher decline rates. An audit detects missing or poorly formatted fields in the authorisation request, such as incorrect address verification (AVS) or card verification value (CVV) data.
Correcting these technical errors directly improves the success rate of legitimate transactions, impacting the bottom line without needing additional marketing spend.
Identification of Hidden Costs
Payment processing statements are notoriously opaque. An audit breaks down the effective cost of each transaction, exposing hidden margins or misapplied interchange rates.
By understanding the true cost of acceptance across different card types and regions, businesses can renegotiate contracts with processors or switch to an interchange-plus-plus model that offers greater transparency.
Use cases
Cross-border Expansion
Merchants moving into new territories use an audit to determine if their current UK or European acquirers can support local payment methods and competitive FX rates in the target market.
Post-Merger Integration
Following an acquisition, an organisation may find itself with multiple disparate payment gateways. An audit provides a blueprint for consolidating these systems into a unified payment orchestration layer.
High Decline Rate Remediation
A merchant experiencing a sudden spike in 'Do Not Honour' codes may use an audit to investigate if their MCC is misclassified or if their 3DS configuration is failing.
Contract Renewal Preparation
Before entering negotiations with a PSP, a merchant conducts an audit to gain a precise understanding of their volume profiles and transaction patterns to secure better commercial terms.
By the numbers
Typical improvement seen when technical errors and suboptimal routing are corrected following a thorough stack review, depending on the baseline maturity.
Industry range for reduction in processing fees when merchants transition from blended models to transparent pricing or consolidate redundant providers.
Standard reduction in legitimate transactions blocked by fraud filters after refining risk thresholds and rule sets during an audit process.
Related terms
Talk to our team about a live rollout on your acquiring stack.
What you get with Payment stack audit
- Verification of card-on-file tokenisation protocols to ensure data portability between different payment providers.
- Analysis of 3D Secure 1.0 versus 2.2 traffic to optimise friction and exemption usage.
- Detailed assessment of MCC assignments to ensure correct interchange tiering and scheme compliance.
- Identification of unnecessary intermediaries in the payment flow that increase latency and failure points.
- Review of dunning management and retry logic for recurring billing models and subscription cycles.
- Evaluation of fraud scoring tools to minimise false positives while maintaining a low chargeback ratio.
- Comparison of settlement timeframes across acquirers to improve corporate cash flow and working capital.
- Assessment of alternative payment method (APM) penetration and its impact on the total checkout conversion.
- Investigation of partial authorisation support and its effectiveness for specific retail or service sector merchants.
- Validation of merchant descriptor accuracy to reduce customer confusion and subsequent retrieval requests.
A short scoping call, then a written plan for your MIDs.
Questions about Payment stack audit
What is the typical lifecycle of a payment stack audit for a mid-market merchant?
A comprehensive audit generally spans four to six weeks. The first phase involves data ingestion, where historians and transaction logs from all gateways and acquirers are gathered.
This is followed by a two-week analysis period where consultants categorise decline reason codes and map the cost of each transaction against scheme fee schedules. The final stage involves a technical review of the current API integrations to ensure they meet modern standards like PSD2.
The result is a report detailing specific technical and commercial areas that require immediate attention to stabilise or improve performance.
How does an audit distinguish between technical failures and issuer declines?
Auditors analyse the raw response codes returned via the gateway. Technical failures often manifest as timeouts or gateway errors (standard 5xx or specific PSP codes), whereas issuer declines provide codes such as 05 (Do Not Honour) or 62 (Restricted Card).
By correlating these codes with transaction metadata, auditors can identify if a decline is due to a merchant's poor data quality, such as missing CVV, or if the issuer's risk engine is rejecting the transaction based on the profile of the cardholder.
Can an audit help in transitioning from blended pricing to interchange-plus-plus?
Yes, an audit serves as the necessary evidentiary phase for this transition. Blended pricing often masks the underlying costs of different card types, such as corporate or premium cards.
By auditing transaction history, consultants can calculate what the costs would have been under an interchange-plus-plus (IC++) model.
This data allows the merchant to see the exact margin the PSP is taking over the scheme fees and interchange, providing the leverage needed to request a more transparent and often lower-cost pricing structure.
Is a payment stack audit required for PCI DSS compliance?
While not a formal requirement for PCI DSS certification itself, a payment stack audit often uncovers security gaps that would impede certification.
It examines how sensitive data flows through the environment and whether the merchant is successfully offloading risk via hosted payment pages or iframe integrations.
By identifying exactly where primary account numbers (PAN) are being handled, the audit ensures that the merchant's PCI DSS scope is as narrow as possible, reducing the cost of annual assessments.
How frequently should a large-scale enterprise perform a payment audit?
It is generally advisable to perform a full audit annually or after any significant change to the infrastructure, such as adding a new gateway or expanding into a new continent.
Frequent audits are particularly important in the context of changing regulations such as PSD3 or updates to scheme rules introduced by Visa and Mastercard.
Regular reviews ensure that the payment stack remains optimised against shifting benchmarks in authorisation rates and that the commercial terms remained aligned with the merchant's current processing volume.
What role does Merchant Category Code (MCC) analysis play in the audit process?
The MCC is a primary factor in determining the interchange rates applied by schemes. An audit verifies that the merchant's business activities are correctly classified.
Misclassification can lead to higher interchange costs or increased scrutiny from acquirers, which can result in higher decline rates or even fines.
In some cases, a merchant may be eligible for a lower-cost MCC if their business model has shifted, and an audit identifies these opportunities to re-classify and save on every transaction.
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