Case Study 02 — Billing

Simplifying Subscription Billing Through Delta Invoicing

Duration 4 months

Role Lead Designer

Scope Invoice & Billing

Stakeholders Cross-functional

01 / Context

Executive summary

Customers frequently contacted support because they could not understand why their subscription invoices differed from expected amounts.

While investigating customer complaints, I discovered that the issue was not merely an invoice design problem but originated from the underlying billing logic. The existing invoicing system generated credit memos and replacement invoices whenever customers modified subscriptions mid-contract. Although financially accurate, the resulting documents were difficult for customers to understand.

The problem statement

Redesign the invoice PDF with more information, as billing-related support inquiries consistently ranked among the top customer service issues — with a significant proportion categorised as Invoice Comprehension Issues.

02 / Discovery

Investigation

Rather than assuming the invoice PDF was the problem, I started by investigating all available customer feedback sources to understand the nature of the issue. I reviewed support tickets, billing dispute cases, customer satisfaction surveys, and account management escalations associated with the "Invoice Comprehension Issue" category.

At first glance, most customers expressed the same concern: they did not understand the amount they were being asked to pay. However, as I segmented and analysed the cases, it became clear that invoice confusion was only a symptom of deeper systemic issues within the billing experience.

The analysis revealed recurring patterns that accounted for the majority of customer inquiries and ultimately shaped the design strategy:

Triggering Events

Quantity changes — addition or removal of any add-on — and subscription modifications such as upgrades, downgrades, or cancellations.

Inconsistent Information

Quoting did not match the invoice at checkout stage. Users took screenshots of checkout to compare against their invoices.

Comprehension Issues

Both scenarios created invoice confusion, leading customers to raise billing inquiries with support.

The current process

Refined problem statement

The investigation revealed that invoice comprehension issues were not solely caused by the invoice design itself. Customers struggled to understand how subscription changes translated into billing outcomes due to inconsistencies across checkout, billing logic, invoice communication, and the sequence of billing documents generated.

The challenge was therefore redefined — from:

"How might we redesign the invoice PDF?" to:

"How might we create a transparent and consistent billing experience that helps customers understand what changed, why they are being charged, and how the final amount was calculated across every billing touchpoint?"

If addressed correctly, it would solve:

Simplifying quantity changes
Improving comprehension — consistent information across multiple touchpoints
Reducing document clutter
Addressing operational inefficiency

03 / Strategy

Challenges

What began as an invoice redesign quickly evolved into a broader billing experience initiative. Research revealed that invoice confusion originated across multiple touchpoints — each stage compounding the confusion of the one before it:

Stage 01

Checkout flows

Quoted amounts at checkout didn't match the final invoice, so customers lost trust in the numbers from the very first step.

Stage 02

Billing logic

Mid-contract changes triggered credit memos and full replacement invoices — financially accurate, but opaque to customers.

Stage 03

Document sequence

Customers received a stack of documents for one simple change, with no narrative explaining what changed or why.

Result: confused customers raised billing inquiries with support — making invoice comprehension a top service issue.

Solving it meant working on two fronts at once:

Aligning multiple teams around a shared solution

Invoicing, checkout, and account teams each owned a piece of the experience. Any fix required a shared definition of the problem and a common billing model across all of them.

Prioritising billing events that couldn't be addressed simultaneously

Quantity changes, proration, seats, and tier upgrades all behaved differently. They had to be sequenced by customer impact rather than tackled in one release.

Service blueprint — the current process vs Delta Billing

To manage complexity and deliver value incrementally, the project was broken down into three milestones, each targeting a specific set of high-impact billing scenarios.

Milestones

Three sequential phases, each targeting a specific set of high-impact billing scenarios.

Milestone 1

Delta Billing Logic

Foundational subscription logic change and redesign

New invoice generated only for the delta quantity change
No credit memo for updates — only for downgrades
Consistent information at checkout & invoice
Updated Order PDF with maintained versions
Billing History event updates
Redesign of the existing invoice

Milestone 2

Explaining Proration

HS credits & seats

Logic change: how we calculate proration
Proration explained at different touchpoints — at checkout and at subscription level with Co-pilot
Seats and AI credits quantity changes covered
AI-generated summaries in billing emails

Milestone 3

Extending Coverage

Tier upgrades

Delta Billing logic extended to tier upgrades — the last high-impact billing event left uncovered
Validated against real upgrade paths for the same clarity customers had come to expect

04 / Execution & delivery

Explorations

To evaluate the new billing logic, I explored the problem from multiple angles — testing invoice pattern directions, using AI tools to diverge on layout ideas, and proposing how AI could help customers interpret complex invoices.

01 — Invoice pattern explorations

Pattern studies for communicating delta charges, terminology, and a consolidated future-state invoice — testing how quantity changes and proration could be made self-explanatory on the document itself.

Invoice redesign patterns

Terminology proposal

Consolidated invoice — future state

02 — Checkout exploration

Explorations for surfacing billing details, proration, and subscription changes at checkout — aligning quoted amounts with what customers later see on their invoice.

Checkout exploration

03 — AI-generated inspiration

Designs generated with AI tools to rapidly diverge on layout and explanation patterns — several of these fed ideas into the invoice pattern work above.

04 — AI invoice assistant proposal

A proposal for how an AI assistant could help users interpret invoice PDFs — reading line items, explaining proration, and clarifying why the amount due differs from expectation.