The simple fix is to first try and refresh your page.
If that doesn't work, log out of Thrive and log back in. This will reset your authorization token and should get you up and running again.
The cause of this issue can be different things. Essentially, the error message means that your browser is not authorized to complete the task you are trying to accomplish.
If this error happens frequently (like multiple times in one day), start a chat with us and we can provide additional troubleshooting tips!