Missing certificate in Lync Certificate Store

Hello

I'm trying to deploy an Edge server for our actual Lync environment.

Internal cert installed fine. But for external cert, i'm stucked.

I've made the request, sent it to the certificate authority, then I received a couple of '.crt' files by email.

I've imported all of them in the Trusted Root Certification Authority of my Edge server.

But still I can't assign a certificate because there is only the Internal certificate available in the Certificate Store.

Thanks for any help you will provide