The message “Sorry, server is not available” means the application cannot establish a connection to the server. This can happen in several cases:
There may be a problem on Plant's servers. To check this, please go to the web application. If you managed to log in successfully and see your projects, then the problem is not on Plant side.
If you use VPN, proxy or other applications that may affect the Internet connection, please turn them off and try connecting to Plant again. In case you or your company access the Internet through a proxy connection, please read this article.