Yesterday I thought why my vpn won't connect  in my device , problem can be

Server overload: If that is the case, there are instances where the VPN server you want to connect to cannot drive additional connections. You might want to attempt to log in to a different server.  

Server downtime: This means that the VPN server that you are currently using may have some technical problem or it’s being upgraded at the back end. You should also visit your VPN provider's status page to see if they are aware of any downtimes.