API and System Integration: Connecting Your Software
System integration is the service of writing the connections that let the separate programs in your business exchange data automatically: accounting with e-commerce, CRM with the web form, stock software with the marketplace, the carrier with the order system. Connection analysis, development, error monitoring, logging and technical documentation are all in scope. The goal is to end entering the same data into two programs by hand.
// Who is system integration for?
System integration is for businesses that enter the same information into several programs by hand, or spend hours every day carrying data between them. Manual transfer costs not only time but accuracy: wrong stock, missing invoices, delayed shipments. If the programs already offer APIs, the connection is written once and runs on its own for years. If any of the following sounds familiar, you are on the right page.
- Orders are typed into the accounting system by hand every day
- Web form applications are copied into the CRM and some get lost
- Stock lives in three places: the store, the warehouse software and the marketplace
- Two programs were sold as "integrated" but actually run on spreadsheet exports and imports
We apply the same method to a small business with two programs and a manufacturer with eight systems; only the number of connections and data volume change.
// What is included and what is not
The project runs per connection; each connection is analysed and priced separately. The table below lists what a standard project includes and what stays outside, line by line. The programs to be connected must offer an API; for those that do not, a file-based alternative is evaluated, and that boundary is written plainly in the quote and does not change.
| Work | Standard project |
|---|---|
| Connection analysis: which data, which direction, how often | Included |
| API documentation review and feasibility report | Included |
| Data mapping table (field by field, what goes where) | Included |
| Connection development (one-way or two-way) | Included |
| Error handling: retries, alert email, logging | Included |
| Staging trial and verification with real data | Included |
| Monitoring panel: last run, success rate, failed records | Included |
| Technical document and maintenance guide | Included |
| 60 days of bug fixing after delivery | Included |
| File-based transfer for programs without an API | Priced separately |
| Licence and API access fees of the connected programs | Excluded |
| Fixing bugs inside the programs themselves | Excluded |
If the connection needs a new application, that is described under web application development; connections on the WordPress and WooCommerce side fall under WordPress custom development.
// How does it work and how long does it take?
A simple one-way connection takes 1 to 2 weeks, a two-way multi-field connection 3 to 5 weeks; the duration is written per connection in the analysis report. The connection is first tried on staging with sample data, then run in parallel with real data for a few days; it does not go live until verified. Bug fixing is guaranteed for 60 days after delivery.
Analysis (2 to 3 days)
Programs, API documentation, data fields, direction and frequency are documented; a feasibility report is written
Data mapping (1 to 2 days)
Which field goes where, conversion rules and conflict cases are written in a table and approved
Development (1 to 3 weeks)
The connection is written; error handling and logging set up
Testing and parallel run (3 to 5 days)
Tried with sample data, run in parallel with real data, results compared
Go-live and handover (1 day)
The connection is switched on; the monitoring panel and technical document are handed over
// How is the price determined?
Three variables set the price: number of connections, direction (one-way or two-way) and number of data fields. A one-way 5-field connection from a web form to a CRM and a two-way 40-field connection between e-commerce, accounting and a carrier do not carry the same workload, so we quote from the analysis report rather than a fixed list. The analysis is free and the quote is fixed once the mapping table is approved.
If a program's API turns out to be incomplete, the alternative route and its cost are presented in writing; nothing proceeds without approval. Payment is split across delivery stages. Code and access details are yours.
// Results we have delivered
The three cases below represent different connection types. We do not share client names without permission, so sector and scale are given instead; figures come from the monitoring panel and client measurements. All three connections were verified by Zep Bilisim in a parallel run before going live and handed over with a monitoring panel.
- Wholesaler, stock software with WooCommerce — A two-way stock and order connection; 2 hours of daily manual entry disappeared and cancellations caused by stock mismatches fell from 7% to zero
- Insurance agency, web form with CRM — Applications land in the CRM instantly and are assigned to an agent; lost applications ended and first response fell from 1 day to 2 hours
- Manufacturer, accounting with e-commerce and carrier — Orders are invoiced automatically and shipping labels generated; processing 1,200 monthly orders went from 3 people to 1
Two programs being "integrated" is not a spreadsheet downloaded from one and uploaded to the other. Real integration runs while you sleep and tells you when it fails.
// The team behind the work
The project is led by Caner Zep Çelik, founder of Zep Bilisim. As founder and technical consultant he has worked on API integrations, software architecture and web development since 2020 and has been involved in more than 100 projects. He does the analysis, the data mapping and the error-handling design himself and does not outsource the work.
The technical document is written by the same person: the connection's architecture, the mapping table, what to do in error cases and where the access keys are kept. The document lets another team maintain the connection later.
// When is it not needed?
If an official, working integration already exists between the two programs, rewriting it is unnecessary; we say so plainly in the analysis and recommend configuring the existing connection correctly. If the transferred data is a few records a month and manual entry takes 10 minutes, an integration will not pay for itself; we say that in the call too.
If one of the programs offers neither an API nor file transfer, no connection can be built; a program change is evaluated in that case and we set the order accordingly.
OWASP's API Security Top 10 lists, from an independent source, the security risks we check in every connection we build; our testing step is built on it.
// Frequently Asked Questions
Any program with an API: accounting and bookkeeping, CRMs, e-commerce platforms, marketplaces, carriers, e-invoicing providers, payment gateways, ERP and stock systems, form and booking tools. The analysis reviews each program's API documentation and the feasibility is written in the report; for a program without an API a file-based alternative is evaluated.
Every connection is written with error handling: a failed transfer is retried automatically, and if it fails again an alert email reaches you and the failed record is listed in the monitoring panel. No data is lost; it waits in the queue. Errors are fixed free within the 60-day support period; after that, monitoring continues under a monthly maintenance plan.
When an API provider changes versions the connection can be affected, which is why it is written against versioned APIs with subscriptions to change notices. The monitoring panel shows a drop in success rate immediately. Under a monthly maintenance plan we track and adapt to version changes; on a one-off project the change is quoted separately.
Access keys are stored encrypted, transfers run over encrypted connections and only the required fields are moved. For transfers involving personal data, privacy requirements are flagged in the mapping table and no unnecessary field is carried. Logs are kept on your server, so where each piece of data went is always traceable and written in the technical document.
In a one-way connection data flows from one program to the other; for example an order goes from e-commerce to accounting. In a two-way connection the two programs update each other; for example stock is written both from the warehouse software to the store and from the store to the warehouse. Two-way connections need conflict rules in the mapping table and longer testing.
Manual entry stops the day the connection goes live; a parallel check is recommended for the first week. Time saved and errors reduced are measured in the monitoring panel within the first month. The analysis report writes the estimated saving in hours; at delivery the actual saving is compared, and on a one-off project a short review is sent on day 60.
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