Independent consultant and solution provider focused on ERP, e‑invoicing and DATEV.
I advise mid-sized companies and the public sector on ERP projects, from system selection and data migration to go-live. Where standard software falls short, I build my own solutions, such as the e‑invoicing middleware. René Pfisterer, independent since 2015.
E-invoicing & DATEV: from document to posting batch
Companies have had to receive e-invoices since 2025; from January 2027, issuing them becomes mandatory too. I cover the whole path from document to finalized posting batch: bidirectional DATEV integration (Desktop API/REST), GoBD-compliant and multi-client, documented in two whitepapers. For the technical side there is my own middleware between ERP and DATEV; consulting and implementation work without it too.
- since 2025Receiving mandatory
- 2027-01-01Issuing mandatory above €800k revenue
- 2028Issuing mandatory for everyone
- Create & receive e-invoicesProduce compliant XRechnung and ZUGFeRD invoices from the ERP and process incoming ones GoBD-compliant, into accounting.
- Posting logicTranslate your posting rules into a configurable posting matrix.recipient country×invoice type×tax rate×cost type→account
- AI-assisted pre-assignmentPosting suggestions based on historical data, reviewed and approved by your accounting team.
The middleware
My own middleware sits between ERP and DATEV and turns incoming documents into a DATEV posting batch. What it does in detail is on the product page; it is in development, and I show a demo in an appointment on request.
View the middleware →Projectile implementation: from requirements to go-live
Since 2016 I have been an official Projectile partner of Information Desire Software GmbH: rollouts, version upgrades, customer-specific extensions, and interfaces to DATEV, Salesforce, Diamant and other systems, specified, tested and taken live via REST API.
- Requirements engineeringCapture business requirements and translate them into implementable specifications: data model, business rules, exception handling.
- InterfacesDATEV, Salesforce, Atlatos, Diamant, Rex and more; specified, tested and taken live via REST API, shadow tables or file export.
- Rollouts & trainingBring new customers onto Projectile, accompany existing customers through version upgrades, train key users, go-live with monitoring.
- Projectile HOAIIndustry solution for engineering and planning firms, co-developed on my specifications: fee calculation by service phase, directly in the ERP.
ERP change & migration: from mapping to cut-over
Legacy systems are rarely documented, and data quality is usually worse than assumed. Every migration therefore starts with discovery and data mapping; the target date follows from the findings, not the other way around.
- Discovery & data qualityDocument legacy systems, interfaces and data inventories; expose duplicates, gaps and mapping risks before they get expensive.
- Mapping & validationField-by-field mapping with a clear validation process and test runs against real data.
- Cut-overRunbook, dress rehearsal, migration over a weekend.
- Follow-upMonday morning the business runs, followed by reconciliation; stabilize processes, the team takes over.
Interim project management: leadership, analysis and strategy on demand
When a project needs experienced leadership without creating a permanent position: external project management, program management, requirements engineering and business analysis on a daily-rate basis, also via placement agencies.
Since 2019 I have worked continuously for the German public sector (PD, consultancy of the public sector); from 2017 to 2021 I also served as inhouse consultant at TÜV Rheinland Consulting. Regulated procurement and high documentation standards are my normal working day, not an exception.
- External project managementSteer ERP and digital projects: scope, cost, schedule, decision papers for management.
- Requirements engineeringTranslate business requirements into implementable specifications: data model, business rules, exception handling.
- Strategic advisoryBusiness model, market entry, staffing; currently supporting the build-up of the family business Pfisterer Hausmeisterservice und Handwerk in the Hunsrück.
AI automation where it pays off
I automate routine work in back office and finance: invoice texts, standard emails, management reports, with AI and no-code tooling. Before anything is built, we calculate whether the case pays off; sometimes the answer is no, and that is a result too.
I use these tools myself before recommending them; most recently as product owner and developer of the parking app myPlace Parking (Frankfurt-Hahn Airport), built AI-assisted from requirements to deployment.
- Reporting & dashboardsManagement reports and dashboards with Power BI, SQL and the Projectile query manager: data retrieval, calculation and distribution automated.
- Limits firstWhat AI cannot do, I say up front: make decisions, process unclear rules, solve real customer problems.
Tools: check for yourself before talking to me
DATEV Interface Check
Shows where your DATEV connection loses money and where automation would start.
Start the check →Maturity Check
Where does your company stand on ERP, data and automation? Instant result.
Start the check →Whitepapers
Two published whitepapers on DATEV integration and invoicing logic, free of charge as PDF.
Read the whitepapers →Latest from practice
AI coding agent costs more than the developer: the bill I pay myself
Gartner says by 2028 an AI coding agent will cost more than a developer salary. As a solo consultant I pay that today. Four steps against the token bill.
The ERP Clause Nobody Reads Decides the Ten-Year Cost
An ERP system's ten-year cost is set by five contract clauses, not the software you pick. The Diageo case, the EU Data Act and the pre-signature checklist.
The Autonomy Gap: Vendors Sell Autonomous, Operations Deliver Partial
Vendors sell the autonomous enterprise; operations deliver partial automation. Gartner, DSAG and the Lemvigh-Müller case show the real maturity gap.
AI Tokenomics: Why Your AI Budget Has No Ceiling Anymore
Microsoft Copilot Cowork bills by usage since 16 June 2026. Why the Mittelstand budgets AI by the seat but pays by the token, and how to cap the open line.
Who you will be working with
René Pfisterer, M.A. International Management: consultant and solution provider, independent since October 2015, 15+ engagements across the Mittelstand and the public sector. My role is the translator between business and IT; I will also tell you when something is technically possible but makes no business sense.
Solo by design, with a partner network: for implementation I draw on partners such as Information Desire Software GmbH, for larger consulting scopes on partner firms; smaller solutions I build myself, AI-assisted. Documented handovers, a deputy on long-running projects.
More about me →The next step costs nothing.
30 to 60 minutes, no strings attached: where is the biggest friction, what is the most effective lever, and is a collaboration a fit? Afterwards, on request, you receive a concrete proposal with objectives, scope and cost frame.