Cannot make multiple outgoing calls

[yedmusic1]

Hi, i cannot make more then one phone call while im on the phone i have 2 line key BLF's and nothing happens when i press on it

version 16
fanvil phone

 

[leejor]

...and you manually provisioned the second line appearance?

 

[eddv123]

As @leejor states more information definitely required.

More information about the use case also as there could be another way of achieving what you want.