Integrations aren’t optional anymore when building a B2B software, they’re a must have. It’s often the final factor that can make or break a deal — and the reason a prospect might choose your competitor instead. Yet integrations are time-consuming to build and even more time-consuming to maintain over years.
This article gives you a practical way to frame ROI. While partnership fees can be a factor, the real cost driver is often internal: your team's time and resources. We’ll stay generic (every vendor and API is different), but we’ll ground the math in realistic assumptions for a mid-size B2B software vendor operating in Europe, with employer-side labor costs factored in.
We will talk here mainly about integrations with B2B financial software.
What are the steps to develop an API integration?`
A robust integration follows a predictable lifecycle, even if all companies will eventually adapt it their own way. Multiple roles are involved, with the number of people involved changing based on the company size.
1. Planning & Scoping
Every great integration starts with an clear business goal. The Business Analyst (or Product Manager) formalizes what data and which actions matter, in which direction(s), and for whom. This includes identifying the target API, reviewing contractual or certification constraints, and translating customer workflows into measurable acceptance criteria. For finance use cases, be explicit about VAT behavior, document statuses, reconciliation logic, and chart-of-accounts mapping. Typical questions are concrete: should invoices be pushed into the accounting system? Should e-commerce orders flow into the ERP, and should payments come back? Scoping ends with a prioritized MVP, a signed-off data dictionary, and success metrics to prevent scope creep later.
2. Technical Research & Solution Design
Once the scope is stable, engineering dives into the documentation and the sandbox: endpoints and payloads, authentication (OAuth2 or API keys), rate limits, pagination, webhooks, and error semantics. The team designs the integration architecture—event-driven, scheduled, or hybrid—along with idempotency, retry/backoff strategies, and observability (logs, metrics, traces). A short R&D spike of three to five days to prototype a “happy path” end-to-end (for example: create an invoice, read back a payment) pays for itself by surfacing blockers early and aligning everyone on the real constraints of the partner API.
3. Implementation (Development)
This is where the connector takes shape. Engineers implement authentication flows, transform and validate data, call the right endpoints, and handle failures gracefully under quotas and latency. Domain logic is first-class—currency conversion, tax rounding, period locks, and lifecycle state alignment between systems—so the code stays modular and testable. Security and resilience are non-negotiable: secrets are stored safely, sensitive fields are encrypted in transit and at rest, and the integration exposes meaningful telemetry so Support can investigate without deep dives in source code. Delivery is iterative, with vertical slices demoed and verified as they land.
4. Testing & Validation
Before production, quality must be assessed . Unit tests cover transformation rules; integration tests validate end-to-end flows in staging; and scenario tests use realistic datasets, including edge VAT cases, multi-currency, and batch volumes. The QA engineer leads validation, but engineers remain on the loop to ensure performance and handle negative paths such as 429/5xx bursts, schema drift, or webhook retries. The exit criteria are clear: repeatable success on the critical paths and predictable behavior under failure.
5. Documentation & Enablement
Good documentation compounds over time. Internal docs and runbooks detail endpoints, mappings, error catalogs, and recovery procedures. Customer-facing guides explain how to obtain credentials, configure the connector, and troubleshoot the usual suspects. A short enablement session for Support/CSM equips them to resolve the majority of tickets without engineering escalation, which materially reduces your run cost over the first year.
6. Deployment
Production rollout is done is stages, which constant monitoring . Secrets and environment configuration are secured ; jobs and webhooks are scheduled and monitored; and a feature flag gates exposure to a limited pilot before broad release. Per-tenant configuration is standardized so customers can safely enter their own API keys and parameters. Rollback plans are rehearsed. If the target is on-premise, plan for additional packaging, network allowlisting, and upgrade paths—this typically doubles build-and-run effort versus a pure cloud target.
7. Post-Deployment Monitoring & Maintenance
Go-live is the beginning of the real work. APIs evolve—fields are added, endpoints deprecate, payloads change under load—and customers surface edge cases you did not see in staging. Continuous monitoring detects anomalies early; SLOs define acceptable sync latency and error budgets; and runbooks guide first-line diagnosis. Support handles user questions and configuration issues, while engineering adapts to API changes, fixes defects, and tunes performance as data volume grows. In practice, teams should expect a steady maintenance cadence over the year; underestimating this phase is the main reason integration portfolios age poorly.
What are the costs associated?
Once you understand the steps, the next question is obvious: how much does all of this cost?
While partnership fees or paid API access can factor in, the real cost driver is internal: your team's time — the combined effort of product managers, engineers, QA, DevOps, and support teams.
Here’s a practical way to frame the numbers for a mid-size B2B SaaS operating in Europe, using realistic salaries and employer-side costs.
Baseline Effort per Financial Integration
For a typical accounting or finance connector:
- Initial build → ~30 person-days (Product/BA: 5, Engineering: 15, QA: 5, DevOps: 3, Support: 2)
- Annual maintenance → ~40 person-days (Engineering: 20, Support/CSM: 20)
These are conservative, real-world figures for a mid-size team working with modern cloud APIs.
Salary Benchmarks (2025, France, Mid-Level Profiles)
Employer cost = gross salary × 1.35 (midpoint for social contributions).
First-Year Cost Example
Using ~215 workable days/year:
- Initial build (~30 days) → ≈ €10k
- Year 1 maintenance (~40 days) → ≈ €12.4k
✅ Total ≈ €22k per integration
This cost does not take into account infrastructure expenses, partnership fees, or opportunity cost. Moreover, the integration cost can be doubled if the target software is hosted on a local server (on-premise) rather than in the cloud. In that case, you’ll need to install a local agent to bridge the systems — adding setup, monitoring, and maintenance overhead (learn more about local agents).
Many other factors can make the cost vary:
- Scope → Read-only pulls are cheaper; bi-directional syncs with financial accuracy guarantees cost more.
- Domain complexity → Accounting connectors involve VAT rules, reconciliation logic, and schema-rich payloads; simpler POS or CRM syncs may be faster but more fragmented to maintain.
- Experience & geography → First integrations cost more; new countries require tax and workflow adaptation.
- Opportunity cost → Every sprint spent here is a sprint not spent on core product features — which can impact sales, brand perception, and partnerships.
💡 Tip: If you’re building financial integrations, you could outsource everything to a Unified API provider like Chift (learn more about unified APIs here). One integration gives you access to dozens of connectors, saving you months of development and tens of thousands of euros, while giving you total peace of mind.
Want to estimate your integration costs?
Try our Cost Calculator: it uses the same methodology described in this article (effort in days → FTE fraction → employer cost) and lets you adapt the assumptions to your own context (salaries, scope, maintenance load). In just a few clicks, you’ll get a personalized estimate for your roadmap.
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