For the most part, TeamViewer is able to make connections without any special configuration of a device. However, it is possible that your TeamViewer may indicate a red light and the message Not ready. Please check your connection.
Here are a few things you can check if you experience this alert:
Did your general setup change?
Is your internet connection working? Try to load a webpage or other web-based application
Did anything change on your IT setup?
Can TeamViewer reach the internet?
If not, please open Port 5938 for outgoing connections