This error occurs when the API Token saved in the plugin is not correct or if the Smart Send account has been closed.
- Login to your account and verify that you have a valid subscription
- Check that the API Token in the plugin is correct. The API Token was sent to you in you welcome email, and can also be found in your account here
The error message will tell you both what URL you have currently trying to use the API Token for and what URL you have registred on your Smart Send account.
These URLs have to be 100% identical before the API token will work.
To change the URL on your Smart Send user login and go to the Profile Tab.