How did you install it, and did you read the instructions?
The ‘@’ sign is usually to do with it being a template or using socket activation.
When using socket activation, the service doesn’t start until someone tries to connect. I’m guessing this is a vpn server that other people can connect to via a network?
when the service have the @ only can enable but dont run or check status, if remove the @ can enable, run status and work ok! I see other services with the @ in the name and dont show this issue.