API integration guide
API integration for companies in Spain: complete guide 2026
Published: February 19, 2026
Most modern business operations depend on systems that don't talk to each other. Every time your team exports an Excel from one system to import it into another, you are paying the cost of an API integration that doesn't exist. This guide explains what an API integration is, when it makes sense to build it custom, and how to avoid the mistakes that turn it into a production problem.
What an API integration is and when you need one
- An API integration connects two systems to exchange data automatically without human intervention. When the CRM updates a client, the integration can automatically create the contact in the ERP, the project in the task manager, and the invoice in the billing system.
- Signals you need an integration: your team does the same work twice in two different systems, data is inconsistent between systems because it's updated manually, or critical processes depend on someone remembering to do something.
- Quantify the cost before deciding: sum hours/month spent on manual tasks the integration would eliminate × employee cost/hour. If manual cost exceeds development cost in under 18 months, the integration has positive ROI.
- Most common integrations in Spanish companies: CRM ↔ ERP (Salesforce/HubSpot with Sage/SAP/Navision), payment gateway ↔ accounting, e-commerce platform ↔ warehouse ERP, and marketing tools ↔ CRM.
Integration types: when to use middleware vs. custom development
- Middleware platforms (Zapier, Make, n8n): ideal when data volume is low (<1,000 records/day), logic is simple (field A → field B without complex transformations), and both systems have native connectors. Cost: €0-500/month.
- Enterprise iPaaS (MuleSoft, Boomi, Workato): for companies with multiple integrations needing centralised governance, unified monitoring, and advanced data transformation. Cost: €2,000-8,000/month in licences.
- Custom development: when systems are legacy with no documented API, transformation logic is proprietary and complex, volume is high (>10,000 operations/day), or you need full audit of every transaction.
- Decision rule: if you can model 95% of cases with middleware in under 5 hours of configuration, use it. If you spend weeks configuring workarounds, build custom — it will be cheaper and more reliable.
The mistakes that ruin integration projects
- Not defining the source of truth: when both systems can modify the same data, which one wins? This decision must be in the design, not in error-handling code.
- Ignoring silent failures: an integration that fails without alerting is worse than one that doesn't exist. Implement alerts for every failure type and an integration status dashboard someone reviews daily.
- Not accounting for peak volume: an integration that works at 100 records/day may collapse at 10,000. Design for expected peak, not average volume.
- Forgotten historical data migration: the new integration works for new data, but historical data remains out of sync. Plan historical data migration before launch.
How to protect and maintain an integration in production
- Automatic retry system: every integration must automatically retry failed operations with exponential backoff. Without retry, a temporary destination system failure loses data.
- Dead letter queue: records that can't be processed after N retries go to an error queue visible to the team, not silently discarded.
- Monitoring and alerts: configure alerts for latency above threshold, error rate above 1%, and absence of activity when there should be some (a 'zombie' integration that looks active but isn't processing).
- Integration documentation: data flow diagram, description of each consumed endpoint, transformation logic, and field mapping. Essential when the team that developed the integration is no longer around.
Do you have systems that don't talk to each other and manual processes that could be automated?