An API integration lets applications exchange information or request actions through their supported interfaces. A useful integration project defines more than the connection: it establishes who owns each field, how failures are recovered, and how your team knows the systems agree.
Use this guide when hiring an agency to connect a store, portal, finance tool, operational system, or custom application. The questions apply across vendors, but the actual design depends on each provider's documentation, account permissions, and limits. A connector name alone does not confirm the workflow is supported.
Related service: Business application and integration services- 01Receive and authenticate a request or event.
- 02Validate its data and check for previous processing.
- 03Apply the mapped change to the authorized destination.
- 04Record success or place the failure in a review queue.
- 05Reconcile records and safely replay approved failures.
SECTION 01
Write the data agreement before connecting systems
For each record, list the identifier, required fields, transformations, destination, and permitted update direction. Decide what happens when both systems change the same value. Email addresses and names may change or collide; do not assume they are reliable permanent identifiers for every business record.
Specify acceptable delay. A nightly reporting transfer and a checkout stock check have different needs. Ask the agency to confirm which events, lookup endpoints, bulk exports, and test accounts are available. Missing permissions or plan restrictions can change the scope before any custom code is written.
SECTION 02
Choose a connector, scheduled job, or custom service
An existing connector is attractive when it supports the exact records, authentication, and recovery behavior you need. A scheduled job can suit changes that tolerate delay. A custom integration service may be appropriate when mappings, access rules, transaction volume, or exception handling exceed the simpler options.
A webhook is an event notification sent by one system to another. It can reduce waiting, but its delivery rules are provider-specific. Stripe's documentation, for example, warns that events can arrive more than once and out of order. Ask how the proposed integration behaves under those conditions rather than assuming every event is unique and sequential.
SECTION 03
Worked example: paid orders entering fulfillment
Imagine an illustrative store sending paid orders to a warehouse application. The store owns the customer-facing order and payment reference; the warehouse owns fulfillment status. The integration maps product identifiers, creates a fulfillment request, and returns the warehouse reference to the store.
Now suppose the warehouse creates the request but the response is lost. Retrying blindly could create a second shipment request. The implementation needs a stable operation identifier and a supported way to detect previous completion. Where the destination provides idempotency, repeated requests with the same operation key can be handled without repeating the intended action.
Stripe documents idempotency for its own API; that behavior is not universal across vendors. If the warehouse lacks an equivalent feature, ask the agency how it will check completion and prevent duplicates within the available constraints. The answer should appear in the proposal and test cases.
SECTION 04
Agree what happens when the connection fails
A useful error screen tells an operator which record failed, why it failed, and what can happen next. It should not expose credentials or unnecessary customer data. Separate temporary failures from records that require a human correction; repeatedly submitting invalid data does not solve the problem.
| Failure | Expected handling |
|---|---|
| Temporary provider outage | Retry within agreed limits, then alert the owner without losing the job. |
| Invalid product identifier | Hold the record for correction and show the missing mapping. |
| Duplicate event | Recognize earlier processing and avoid a second business action. |
| Expired credentials | Stop unsafe retries and notify the authorized account owner. |
| Conflicting updates | Apply the agreed source-of-truth rule or route the conflict for review. |
SECTION 05
Test reconciliation and hand over operating access
Test with representative data in the provider's approved test environment where available. Include partial success, delayed events, changed field formats, revoked access, and rate limits. Reconcile source records with destination records so a green connection status does not conceal missing transactions.
At handoff, request the mapping document, code or configuration ownership terms, account register, alert destinations, replay instructions, and API version dependencies. For remote delivery, identify who can respond during the business hours that matter to your operation. Maintenance for future provider changes should be clearly agreed.
Control budget by beginning with one record type and one direction when that solves the immediate problem. Keep essential recovery checks. Contact us for pricing; our application cost guide explains how integrations affect a broader project without treating every connection as equal work.
SECTION 06
Frequently asked questions
Can an agency connect any two applications?
Not necessarily. Feasibility depends on supported APIs or exports, account permissions, vendor terms, required data, and the actions each system allows. Confirm the difficult connection before committing to the full build.
What is the source of truth in an integration?
It is the system authorized to own a particular record or field. Different systems can own different fields, but the update direction and conflict rule should be explicit.
Why do API integration proposals include monitoring?
Connections can fail after launch because of invalid data, outages, expired access, or provider changes. Monitoring and reconciliation help the owner find missing work and recover it safely.
PRIMARY REFERENCES
Sources and further reading
These references cover the standards, platforms, or published prices discussed in the guide. Worked examples and checklists are our editorial guidance.
EDITORIAL METHOD
About this guide
We use AI to assist with drafting and editing. Catapult AI Work is responsible for the published content. Examples illustrate possible approaches; they are not client case studies unless identified as such.
Budget examples are not Catapult package prices. Check linked provider pages for current fees and plan limits before making a purchase.
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