The Ocp-Apim-Subscription-Key is indeed the Subscription key.
Yes, unfortunately either the MSN, Client ID, Client Secret or Subscription Key is wrong.
The message you are getting does single out the subscription key, but you should check if the sub key is for the live or for the test environment. If it is for the test environment, please go to the Vipps settings, choose “Advanced”, turn on “Developer mode” and save. Then return to the settings page and choose the “Developer mode” tab which will appear.
Here you will need to turn on test mode and add the MSN, Client Id and so forth for the test mode account.
Your “live” keys should be stored in the Main tab.
Test mode MSNs/sub keys and so forth do not work in the live environment and vice versa.
Thank you. Worked first time.