I am using OpenProject (Free Version) and trying to use the V3 API to fetch and add work package.

I am getting Unauthenticated message when I am trying to get data using the API.
I tried: 
1. ‘apikey’ as the user name and API key as the password and I get error (see below). 
2. Then I turned off authentication required field (in System settings -> General) and again I get Unauthenticated.

Full message:  
{
   "_type": "Error",
   "errorIdentifier": "urn:openproject-org:api:v3:errors:Unauthenticated",
   "message": "You did not provide the correct credentials."
}