If you get the error message that “The user does not have an API access”, the REST API access has not yet been enabled for this particular user.
The admin of the account has to enable the REST API access for the user.
Please open your account and go to [My account] > [Users]. Click on  for the respective user. The following window will appear on your screen:
Activate the “REST API access” checkbox – a blue tick will appear. Save your changes and log in again on your page.