Add ip address and domain name and associate them

when i try first for adding domain name i face a probelm of adding it from hestiacp interface i got those error
Oops! Something went wrong.

The server encountered an internal error or misconfiguration and was unable to complete your request.

Error Code: 500


Field “Assigned User” can not be blank.
and when i try to select user i didn’t find any user in that field even i already have users so i add directly by command v-add-sys-ip " ip address" “netmask” i add new user and domain name a and copy its dns in the hostname provider but got error
ERR_CONNECTION_REFUSED i don’t know what the issue here so i need your help please cause i search too long and i don’t find any problem like that.