Access Denied. (Code 3000)

I am only using the Sandbox API from PostNL ( Via WooCommerce ) eveything seems to work but I am trying to print Labels for my test orders to get a look and feel oif them but I keep getting Access Denied. (Code 3000) when I click to print.

I also have a product code ( which I have not used ) is this issue only because I am using the sandbox API key ?

Would I have them some problem using the production API key ? Not so happy in using that for testing.