The Apigee Professional API Engineer designs, builds, and maintains API proxies. The API Engineer’s responsibilities include cross-cutting business concerns like authentication, authorization, monitoring, logging, governance, and documentation. API Engineers also consider API design features like consistency, usability, and versioning. Finally, the API Engineer measures and drives success of the API program and is responsible for the documentation, promotion, and evangelism of its products.
Note: Google has also officially retired this certification. (https://support.google.com/cloud-certification/answer/10343239?hl=en&ref_topic=9433464). The Apigee UI also has totally changed.