Custom API integration services for connected business systems

StackEndBox designs and implements custom API integrations for businesses connecting existing applications, repairing unreliable data handoffs or exposing an API for their own product. We scope the connection, field mapping, failure controls, deployment and operating handover as one engagement. The first release proves one agreed business workflow, rather than adding every available connector.

We agree the connection's direction, timing and source of truth before building. A new enquiry becoming a CRM record is an event-driven workflow. Keeping selected records aligned in both directions needs conflict and deletion rules as well. The right scope depends on your actual APIs, account permissions and operating volume.

Who this is for

• Teams whose tools do not share data and rely on manual copy-and-paste.
• Products that need to connect to payments, CRMs, messaging, calendars or partner systems.
• Operations leads who want recurring tasks completed automatically and recorded.

When this is the right fit

• The same data is entered into two or more systems, and mismatches cause errors or delays.
• A process crosses several tools and depends on someone remembering to move it along.
• Your product needs to expose an API for customers or partners.
• A ready-made connector exists but is too limited, too costly at your volume, or lacks the failure handling you need.

What we build

• API design and backends

  Clear, documented interfaces for your own product and for other systems to use.

• Third-party integrations

  Connections to payments, CRMs, messaging, calendars, email, storage and other services you rely on.

• Webhooks and event handling

  Reliable handling of incoming events, with checks so duplicates and failures are managed.

• Data mapping and synchronisation

  Records kept consistent across systems, with a clear source of truth.

• Process automation

  Repeated tasks such as confirmations, follow-ups and document filing turned into automatic steps.

What you get

• A reviewed data-flow map covering field ownership, record matching, direction, timing and deletion rules.
• The integration or automation running in production, with credentials stored securely.
• Agreed duplicate and failure controls, with saved operation references and a way to check an uncertain result before retrying.
• Alerts to a named person or channel when something needs attention.
• Documentation, test evidence and operator recovery instructions, plus API documentation if we built an interface for others to use.

Build, buy or hybrid?

Many integrations do not need custom code. The trade-offs look like this.

• Built-in connectors

  If both tools offer a supported integration that does what you need, use it. It is maintained by the vendor and costs the least effort.

• Automation platforms

  Hosted workflow tools are quick for simple, low-volume flows. Costs, rate limits, error handling and complex logic are where they tend to strain.

• Custom integration

  Fits when volumes are high, logic is intricate, reliability matters, or the integration is part of your product. You own the code and the behaviour.

When not to hire us. We are probably not the right choice if a built-in connector or a simple automation already does the job, or if a tool has no usable API and the only route is fragile screen scraping that you are not willing to maintain.

What affects the cost of API integration

We do not publish prices, because cost follows scope. These are the drivers that move it most.

• Number of systems

  Every extra system adds mapping, testing and maintenance, and the connections between them multiply.

• Quality of the APIs

  Clear documentation and sensible rate limits make for a smaller job. Poor or missing APIs need workarounds.

• Volume and timing

  Real-time sync of many records is harder to build and run than a nightly batch.

• Data mapping

  How different the systems’ records are, and which one is the source of truth.

• Failure handling

  Retries, duplicate protection, logging and alerts are what make an integration dependable, and they are part of the work.

• Built-in connector or custom

  Where a supported connector does the job, it costs the least. Custom code is for what connectors cannot do.

• Maintenance

  Third-party APIs change, so integrations need upkeep, agreed separately.

How we work

We map the systems and the process first, design the approach, build the integration and verify permissions, edge cases and failure handling before it goes live, then monitor it in production. Because third-party APIs change, rate-limit and fail, we plan for versioning, retries and clear logging from the start, and document what the integration does so your team can support it. We also agree up front what counts as a failure worth alerting on, so the integration neither stays silent nor floods your team.

What we need from you to start

• The list of systems to connect and which one should be the source of truth for each kind of record.
• Product and plan names plus public API documentation. We agree authorised sandbox access through a secure process after scoping. Do not send passwords, tokens or private records in an enquiry.
• A description of the manual process today, including the exceptions people handle.
• Expected volumes, such as records per day, so we can design for them.
• Who should be alerted when an automated step fails.

Technology

• TypeScript
• Node.js
• Python
• PostgreSQL
• Supabase
• Stripe
• HubSpot
• Google Workspace

Frequently asked questions

What are API integration services?

Services that connect software so systems exchange data automatically. At StackEndBox that covers mapping the systems, building the connection, handling failures and retries, and monitoring it after launch.

When is a custom integration better than Zapier or Make?

When volume, logic, reliability or data handling outgrow them. For simple, low-volume flows, tools such as Zapier, Make or n8n are often the right answer, and we will say so.

How much does API integration cost?

It depends on scope. The drivers are the number of systems, the quality of their APIs, volume and timing, data mapping, failure handling and maintenance, listed under “What affects the cost of API integration”.

What is an API integration?

It connects two pieces of software so they can exchange data automatically, instead of someone doing it by hand.

What happens if a connected service fails?

We design for it: failed events are handled and retried where appropriate, so work is not silently lost, and someone is alerted if it persists.

Can you automate a process that involves several tools?

Yes. We build workflows that span your tools and finish with a record of what was done.

Can you work with a tool that has a poor API?

Often. We assess what the tool exposes and choose the safest way to connect it, and we tell you where limits make a requirement impractical.

How are credentials and customer data protected?

API keys are kept out of source code and given the narrowest permissions the integration needs. We only move the fields the process requires, and agree with you where logs and copies of data are kept.

Who owns the integration code?

Ownership of the code and documentation is agreed in the project scope before work starts, along with who holds the accounts and keys.

Do you maintain integrations after launch?

Third-party APIs change, so integrations do need upkeep. We can monitor and maintain them under an ongoing arrangement agreed separately.

How do we begin?

Book a call or email us the systems involved and the process you want to fix. We reply with the questions that determine scope and feasibility.

Related services

• CRM & ERP Integration: for field ownership, sales-to-operations mapping and reconciled CRM/ERP cutover.
• AI Document Processing: when inputs begin as PDFs, scans or forms rather than structured API records.
• AI Systems & Agents: when a step in the workflow needs reading, classifying or drafting by a model.
• Custom Client Portal Development: when connected records need to appear in an account-specific customer workspace.
• Custom Software, Web Apps, CRM & Internal Platforms: if the process needs its own application, not only a connection between tools.
• SEO, AEO/GEO, Google Ads & Meta Ads: to tie web forms, CRMs and campaign data together for measurement.
• AI Automation Services: when the process needs a model to read, classify or draft, with human approval.

Decision guides

• API integration project checklist for business teams: Scope an API integration before hiring a developer. Define data ownership, sync rules, failure recovery and acceptance checks with a reusable project brief.
• Client portal acceptance checklist for service businesses: Use pass-or-fail checks for client access, documents, support and failed requests before accepting a custom portal. Includes a reusable review template.
• AI Agents vs Deterministic Automation: When to Use Each: A practical decision tree for choosing between rule-based automation, an AI step inside a workflow and an AI agent, covering cost, latency and failure modes.
• Custom Software vs SaaS: How to Decide What Your Business Actually Needs: Custom software or SaaS? A practical framework covering fit, integrations, data ownership, total cost, vendor risk and the hybrid option, plus a checklist.