Proof of concept (PoC): Implementation of a subscription service with billwerk


[>German Version] Times Square. Loud, colourful and hectic. One billboard is more eye-catching than the next, and they’re all demanding attention and promising everything you could ever wish for. Without someone to guide you through, you soon feel lost and overwhelmed.

The market for subscription management products could be described in a similar way. It’s equally non-transparent and difficult to navigate. Especially once the initial contact has been established, beyond the world of product demos and sales presentations. That’s why this blog post takes a closer look at billwerk, a state-of-the-art subscription management platform. We collaborated with billwerk to implement a PoC in order to test their product and its integration in practice.


The joint path to a subscription service and the team structure

A small multi-disciplinary team was involved made up of colleagues from doubleSlash and billwerk. We worked collaboratively using timeboxing and other agile methodologies. The PoC for the subscription service included the following phases:

1. Agile implementation of the PoC:

      • Kick-off
      • Exploration / IT Design:
        Use cases, functional data model, system overview, interfaces
      • PoC implementation
        Technical setup, implementation based on design artefacts, testing

2. PoC evaluation


The PoC – a fictitious vignette service

As a use case for the joint PoC, we implemented a fictitious vignette service. The use case focuses primarily on setting up the subscription service in order to evaluate the functional and technical coverage offered by billwerk’s product. The implementation of further legal requirements, such as the recipient location principle, was deliberately excluded from the PoC. The vignette service offers two different tariff types: Family and Flex. The Family tariff consists of a base fee of €10 per month. Customers who opt for this subscription can then purchase the vignette for Austria or Switzerland as well. The price and validity period are the same as the actual market price. The added value of the subscription is the fact that the vignettes are also valid for other family members. The base fee for the Flex tariff is higher but offers greater flexibility, since a valid subscription for the Flex tariff lets you purchase vignettes on a daily basis.

PoC for Subscription Management Vignette
Figure 1: The proof of concept for the vignette subscription service; Source: Own illustration.

The subscription service with billwerk

Before we started creating the PoC, we had a meeting to compare and define our common understanding of the subscription management domain.

Subscription management systems at doubleSlash
Figure 2: Subscription management systems at doubleSlash are divided into four core components; Source: Own illustration.


It soon became clear that there were no major deviations and so the way was clear for the PoC. As is common practice in project management, we held a joint kick-off meeting to discuss the PoC use case in detail. We were able to start with the IT design and implementation soon after this first meeting. The smooth staging of a test environment and the relevant access permissions further accelerated the start of the project. The ‘API First’ approach at billwerk enabled us to implement the solution quickly. Special mention should be made of the clear and intuitive UI which contributed greatly to our understanding of the application. The ‘API First’ approach allowed us to explore the Rest API almost playfully, making it a valuable addition to the documentation. After the initial kick-off, a few more meetings followed so that we could learn more about the application and clarify some details. Perfect for integrators like us.
Besides the functional coverage of the application, we were also able to take a look behind the scenes. This allowed us to get to know some of the team at billwerk, and there was always someone available to answer all our questions. This resulted in a productive exchange of ideas and some extremely interesting discussions. We found it particularly positive to see that billwerk places such high demands on its product in terms of quality. This is a key criterion for us since quality is the basis of any good software product, after all. It also has a positive effect on the integration and implementation of customer-specific requirements. In addition to the quality, we were also impressed by the options billwerk offers its customers with regard to operating the subscription service. It can be hosted in a public or private SaaS environment or even as an on-premises solution. This offers potential customers a high degree of flexibility.

Shared enthusiasm for subscription services makes for good collaboration

Throughout the implementation, our collaboration was very much an equal partnership. Our shared passion for subscription management resulted in a very open exchange. billwerk explained their design decisions efficiently and transparently, particularly in the case of features not yet included in the standard product. A good example is billing based on individual usage data. billwerk supports usage-based business models and usage-based billing, but the usage data must first be converted into a format that can be understood by the billwerk solution. Assuming in the Flex tariff described above that the price of the daily vignette depends on the time of day it was purchased, the correct usage data record needs to be passed on to billwerk rather than the application itself recognising which price applies based on the time of day. Cases like these can become extremely complex and are highly customer-dependent. Given the high complexity, billwerk decided to exclude this feature from the standard solution for the time being. This is typical of the company’s aspiration to offer a comprehensive and carefully planned solution as opposed to a feature that only covers half of the use cases. We know from experience that their decision makes sense, as we often find in our integration projects that transformations are extremely customer-specific and can rarely be reused.


Interesting change of perspective: The PoC experience from billwerk’s point of view


Summary: Successful PoC for subscription services

We were very impressed by billwerk as a company as well as by their product, and we can safely say that the PoC was successful. We can definitely imagine working with billwerk again in future projects to create more complex subscription models. The functional scope is well tailored. What’s more, billwerk provides excellent online documentation explaining the subscription management business model and the related terminology in detail. We got the impression that billwerk appreciates our feedback and takes it very seriously, and they show a keen interest in constantly improving their product. This impression was reinforced in our joint retrospective meeting.



What are the main factors to consider when selecting and integrating a subscription management system? Which provider is the best match for your IT infrastructure and billing systems? Our whitepaper includes a comparison of different billing platform providers tested by doubleSlash.

Download the german whitepaper



Read more about our proof of concept experience with the billing platform killbill:  To the POC with killbill

Subscription business models in action:
Here you can find insights into our projects with customers in the subscription management environment: To the doubleSlash Usecases


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