Event Rule Transform and compose node expression not working

[Naresh Kumar G2]

I have a requirement to extract Host Name from a json variable. The issue is the Host Name field may be placed any where in a statement. 

Example: 

Host Name:TEST, Group Name:TEST GROUP

Host Name:TEST2

Others, Host Name:TEST3

Following Regex works fine using regex101 for my example but it is not working when I used it in ServiceNow. it always says <<UNKOWN>>

https://regex101.com/r/HoKx0B/1

.*Host Name:([^,]*)

Could someone help me to identify the issue why ServiceNow is not accepting the regex.