REST API Postman - error The API key does not belong to the projec

I’m attempting to use Postman to get test data back to incorporate into my server.

As a test, I ran this as a GET

https://api.revenuecat.com/v2/projects/{project_id}/customers/{customer_id}

Replacing {project_id} with my project id from general → project id

And using a customer_id from the overview dashboard.

However I receive this error:

How can this be resolved.

Thanks