Editorial illustration.
Originally published 16 June 2023; rewritten and reviewed on 15 October 2026.
I followed the Kentico Web API integration steps and still reached an error instead of a working endpoint. In this case, the issue was not the route I had just added. The separate API project referenced newer Kentico libraries than the CMS installation it needed to work with.
Compare the installed versions first
A shared namespace does not establish binary compatibility. I would record the CMS version and hotfix level, then compare the package and assembly versions loaded by the API project. Check dependency resolution and the deployed files, not only the version displayed in the package manager.
The original article linked instructions across Kentico 8.1, 8.2, 9, 10, 11, 12 and 13. Those guides describe their respective products; they are not interchangeable steps for every release.
Choose the smaller compatible change
For the project described in the original post, aligning the API project’s libraries with the installed CMS was the preferred direction. Upgrading the entire CMS simply to satisfy a new API reference would have introduced a larger change into modules that were already working.
That is a project decision, not a universal instruction to downgrade packages. Check the supported combinations and security requirements for the actual system. Keep a record of why the chosen versions belong together.
Test the API as a separate boundary
Once it starts, verify authentication, authorisation, response shape and failure handling. An endpoint that can load CMS types is not automatically safe to expose. Return only the records and fields the caller is permitted to receive.
The diagnostic habit I took from this issue is simple: when integration instructions appear correct, inspect the shared dependency contract before rewriting the feature. The fault may be in what the two projects load, not in the line that first displays the error.
Related reading
Images from the original article
The following images are retained as historical context; interfaces and configuration options may have changed.
