These errors indicates that was an issue trying to renew the SSL certificate generated by TSplus. This SSL is based on Let's Encrypt services. 

Your domain name must be available from outside and redirected to your TSplus server, you should be able to see your TSplus application portal when entering your domain name. 

The port 80 must be opened for inside and outside traffic.

This issue can occur if Let's Encrypt IP's are blocked from your firewall or proxy, the domain to be added are the following :

Using any other web server than TSplus web server is not supported with the use of the SSL certificate generation tool provided with TSplus.
So make sure to disable any Apache or IIS if present. Using a dynamic DNS is also not supported with the SSL generation tool.

If the above have not solve your issue, please provide us with the content of the folder below from your TSplus server : 
C:\Program Files (x86)\TSplus\UserDesktop\files\.lego\logs

Starting from, your logs will be placed in :

C:\Program Files (x86)\TSplus\UserDesktop\files\cert\CertificateManager.log