not working config:
tlscertfile=/usr/share/ombutel/certificates/pbx2.raven.kz/bundle.pem
tlscafile=/usr/share/ombutel/certificates/pbx2.raven.kz/chain.pem
working config(self-signed) :
tlscertfile=/usr/share/ombutel/certificates/pbx.raven.kz.pem
tlscafile=/usr/share/ombutel/certificates/ca.crt