I selected the Authentication type as API Key for my rule in API Gateway. But why am I still getting the 'No privileges to perform this action' error?

If you enabled the API Key-based authentication, the authentication is handled by an API key generated by Catalyst for your project automatically. You need to pass the API Key value with the keyname ZCFKEY along with the request header or as a query parameter.

The API Key is the same for all projects in the development environment. When you deploy a Catalyst project to the production environment, Catalyst will provide you a different API key for production. You will therefore have individual API keys for each project in the production environment.