9. Assumptions and Open Inputs
The brief named four candidate APIs and a design rule (pick a job businesses repeat forever). It did not give a team, hours, geography, language, stage or budget. Here's what I assumed, and how the verdict changes if each assumption is wrong.
9.1 Assumptions made
| Input | Assumption used | If actually different… |
|---|---|---|
| Stage | Idea. No code, no users, no revenue. | Any existing API customers change the channel plan. Send their data. |
| Team | 1 founder, technical (backend, APIs, XML), no stated tax or e-invoicing background | A founder or partner with German e-invoicing, ERP or tax-software experience raises every rung by ~5–10 points. |
| Hours per week | Two versions are given: ~15 hrs/week and full-time | Below ~10 hrs/week, the Q4 2026 window will be missed. Cut the $1k odds by about a third. |
| Language | Founder doesn't necessarily read German | This is condition 1. Without German capability (own or paid), multiply the odds by ~0.6. |
| Location | Outside the EU is possible | Workable with a merchant of record, EU hosting and a DPA. It adds trust friction for German buyers. |
| Pricing | None stated. The recommendation is €29 / €79 / €199 plus overage, blended ~€65 ≈ $75 | Below ~€40 blended, churn benchmarks and the pre-mortem (doc 05) say the ceiling falls sharply. |
| Buyer | Companies invoicing German B2B from their own code | If the real audience turns out to be no-code users, this becomes the ScreenshotOne curve again. |
| Market size | 20,000–50,000 companies invoicing from own code (analyst estimate) | If it's under 10,000, $10k+ needs France early. If it's over 100,000, the $10k odds improve. |
| Mandate stability | Germany keeps 1 Jan 2027 / 1 Jan 2028. No postponement found as of 30 Sept 2026. | A postponement delays urgency by about a year. The ViDA 2030 cross-border rule and France keep demand alive. |
| Churn | ≤2.5% monthly revenue churn after month 6 (judgment, not a benchmark) | At 4–5%, the $20k rung roughly halves (see the churn check in WHAT-TO-DO-AND-AVOID.md). |
| Funding | None, and none needed | Doesn't change the product advice. |
| Exchange rate | €1 ≈ $1.15 | Small effect on the customer counts. |
9.2 Inputs that would change the verdict most (please supply)
- Hours per week available, and for how long you can hold them.
- German-language ability: yours, or a partner you can pay.
- Any access to German developers, agencies or SaaS founders (network, community, past employer).
- Existing domain experience: have you built billing, invoicing, ERP or tax software before?
- Your location and billing setup: EU entity, or a merchant of record.
- Budget for a German tax adviser review (~€500–1,500 one-off, estimate) and professional indemnity insurance.
- Appetite for B2B support. Even a self-serve API gets month-end tickets from finance teams.
9.3 Definitions used throughout
- MRR ladder: the chance of reaching $1k / $3k / $5k / $10k / $20k / $50k MRR by month 24, while profitable at that level (gross margin ≥80%).
- Tier A: $1M ARR within 36 months, ≥70% gross margin, ≥50% month-12 logo retention.
- Tier B: $20k+ MRR within 24 months, profitable, ≥80% gross margin, ≥70% month-3 retention.
- Revenue churn: MRR lost to cancellations and downgrades in a month, divided by MRR at the start of the month.
- Max MRR (ceiling): new MRR per month ÷ monthly revenue churn (Jason Cohen).
- E-invoice: a structured invoice following EN 16931 (XRechnung, or ZUGFeRD / Factur-X at EN 16931 profile or above). A plain PDF is not one.
- Base rate: no verified base rate exists for bootstrapped B2B micro-SaaS. Mobile-app figures (RevenueCat) are shown for scale only.