Phil Leggetter
How Pennylane Streamlined Six Integrations and Eliminated Replay Errors with Hookdeck
Pennylane is building a financial operating system for small and mid-sized businesses across Europe. With Pennylane, entrepreneurs and accountants no longer work from separate tools or versions of data.
Accountants and business teams can work together on invoicing, expenses, payments, bookkeeping, taxes, and cash flow without jumping between systems.
A key part of that system came from Billy, a startup founded three and a half years ago by Aurélien David. Billy focused on building connectors that linked financial software with platforms where transactions originated.
Shopify was the first e-commerce platform that pushed the team toward webhooks, since polling wasn't enough to support high-volume real-time order activity.
Pennylane acquired Billy after working with the team as a customer. Once integrated, the connector workflow shifted from slower periodic checks to real-time event-driven updates.
For accounting use cases, a delay was acceptable. But for e-commerce merchants, every order received needed to generate an invoice in minutes.
“What we do is take every Shopify or e-commerce order and create an invoice in Pennylane.”
The challenge
Pennylane's connector team originally relied on periodic checks to sync order data into invoices. Once the product expanded into e-commerce workflows, timing became critical.
Orders needed to be converted into invoices quickly and reliably, and that shift pushed the team toward webhooks.
“At first, we tried avoiding webhooks and used periodic checks, but once we moved into e-commerce, we needed real-time.”
Shopify became the turning point. Its webhook system sent large volumes of product and order events at unpredictable times. The retry logic created noise, and without visibility, the team couldn't tell whether events failed, arrived twice, or never reached the endpoint.
To troubleshoot, the team stored every webhook payload in their database. The table grew quickly and made debugging slow.
Developers scrolled through long histories of payloads trying to match timestamps and identify gaps. The workflow was fine on paper, but under production traffic, it became difficult to manage.
“We didn't know if we had received a webhook or not. We just hoped everything worked.”
The biggest risk surfaced when Shopify automatically removed webhook subscriptions after repeated errors.
A single failure could slow the system and could even break the integration entirely. Without replay controls or visibility, recovering from those drops would take up valuable development time.
Running and testing callbacks locally also added friction, especially for a small engineering team already spread thin.
What broke the workflow?
- No visibility into received or missed events
- Shopify retries and subscription removals
- Manual debugging from stored payloads
- No controlled replay mechanism
- Local development friction
The solution
Aurélien discovered Hookdeck through developer conversations on X. He follows tooling closely and prefers using reliable infrastructure over building everything in-house.
When Shopify traffic began overwhelming their webhook setup, he started looking for a platform that could handle retries, filtering, and replay without extra operational work.
Hookdeck stood out because it didn't require a rebuild, just a URL swap.
“We wanted a tool between the webhook sender and our app because it gives the developer visibility on what happened.”
Hookdeck gave Pennylane a reliable foundation for real-time commerce workflows. Instead of reacting to webhook failures, the team now builds with confidence that events are recorded, traceable, and recoverable.
Visibility and developer control
Before Hookdeck, debugging meant scrolling through internal webhook logs and hoping nothing was missed. With Hookdeck, the team gained full visibility into every webhook lifecycle.
They could see what arrived, what failed, and what was retried. One change made a difference: developers could forward live production traffic directly to localhost. This removed the need for tunnels and made local debugging faster and predictable.
“The first thing that caught my interest was being able to receive production webhooks on localhost without using tunnels. We could plug the production URL directly, listen to events, and forward them to local development.”
Queuing and guaranteed delivery
As the connector expanded to more platforms, webhook traffic became unpredictable. With Hookdeck in place, every event was captured and queued. If an endpoint slowed or paused, Hookdeck held the payload until the system was ready.
The team no longer needed to rely on Shopify's retry model or risk missing invoices when errors stacked up.
Filtering unwanted webhook noise
Legacy webhooks and unused integrations created traffic that no longer belonged in the system. Hookdeck's filtering addressed this. Instead of paying for function invocations or sifting through cluttered logs, the team blocked unwanted requests before they reached their stack.
Smooth rollout and long-term fit
Adopting Hookdeck required no major infrastructure changes. The team migrated sources one by one and now runs six platforms behind the same webhook control layer.
The result
Since migrating nearly all webhook sources to Hookdeck, webhooks have stopped being a daily concern. Shopify and WooCommerce order events, plus billing signals from tools like Lago, Hyperline, and Sellsy, flow through one place.
When something goes wrong in the Pennylane codebase, events are still captured and ready to replay. There is no guessing about whether Shopify silently dropped a subscription after repeated failures.
Faster debugging and easier onboarding
Developers now start from a single dashboard when they suspect an issue. They see recent webhooks, filter by source, inspect bodies, and replay what matters.
New engineers on the connector team can learn how the system behaves by watching real traffic in Hookdeck and forwarding it to localhost, rather than wrestling with logs.
“We identified real issues faster with Hookdeck than we would have without it.”
One control plane across all connectors
As Pennylane's connector product grew, different platforms brought different webhook quirks. By routing Shopify, WooCommerce, Lago, Hyperline, Karlia, and Sellsy through Hookdeck, the team now treats them as one system.
Each source is visible in the same UI, with the same alerting and replay story. When they like how a setup behaves, they replicate the pattern for the next connector instead of starting from scratch.
Less time firefighting, more time on product
Before Hookdeck, the team had to guess whether Shopify had deleted a subscription after too many failures. Now they can see issues early through Hookdeck alerts and history, then replay what matters.
The connector table in their own database no longer needs to act as a crude log store. Developers spend less time digging through past payloads and more time improving how orders turn into invoices for merchants.
The impact on Pennylane's connector platform
With Hookdeck in place, the team treats webhooks as stable, observable infrastructure rather than a fragile edge.
- High confidence that e-commerce orders become invoices without silent gaps
- Clear the replay path when Shopify transforms or mapping logic changes
- Reduced guesswork when investigating merchant issues
- Lower serverless cost from blocking unwanted legacy webhooks
- A standard entry point for any new e-commerce or billing source
A roadmap built on stability
Hookdeck gave Pennylane a clean foundation to grow from. Instead of working around unreliable webhook streams, the platform now processes events consistently with clear visibility and control.
The team can add new integrations without rebuilding the system or dealing with unexpected retry loops, duplicate payloads, or missing events.
Looking ahead, Pennylane plans to move to a Terraform-managed configuration and improve filter safety to avoid accidental event loss. With replay, filtering, and queueing already in place, the team now builds with ease and treats webhook traffic as a solved problem.
How Pennylane will build from here
- Terraform workflow to protect the configuration
- Advanced dedupe to lower noise
- Faster onboarding for new webhook sources
- Stable replay-first debugging workflow
“I'm happy with how the product is evolving, especially the deduplication work. It solves a problem we were already dealing with in our Shopify webhooks.”
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