Grandstream ring before freepbx?

Hi ,
new by this.
( Sorry for my bad english, i’m french speaking )

Hi have a Grandstream 2020.
Account1 is set, and can call in and out.

My problem is,
if someone call to asterisk, the persone get the IRV, but my phone ring to…???
i need always to set the phone on DND…

How can i get that customer call to Freepbx and that Grandstraem NOT ring together whit freepbx.?
I know, it must be somethings in configuration on grandstream i think .?
Kill me if i’m wrong

Thx fo your Tips.