The only thing you can do is to reinstall the application since the official website is not available, thus making it impossible to obtain troubleshooting information. I also advise choosing other messenger application since this one appears to be discontinued.
You can use Facebook Messenger or Skype. Facebook Messenger can be used to chat with friends and family while Skype can also be used for business.
-Skype: https://www.skype.com/en/
