Directus - custom API implementation

I'm looking for a experienced Directus developer to implement four APIs that integrate with an PostgreSQL or SQLite database. Two APIs (single key-value pair of JSON payload) require small custom logic. The database will contain three interconnected tables storing application data.

The successful candidate will configure Directus to authenticate and authorize API requests conforming to RESTful standards. To each of theses endpoints, roles/users/CRUD can be assigned individually.

Important: The API responses must be clear and unique to each error. E.g. "message": "The license key is invalid or already activated", is difficult to handle if a customer complains.

Directus experience combined with clear communication and thorough work will be viewed favorably. Please provide portfolio examples showcasing similar integrations you have successfully developed.