Hello. It is first time I am facing with IP telephony and exactly with grandstream, I have in the office 30 phones- they are working, Now I have 3 new phones and need to setup them, I connected them, it got IP by dhcp, I setup by default, number, sip and etc, but it shows as red and not registering. Can you please advise what can I do?
Try using zero-config. You can find the manual on the GS website in the products and resource area. Also, make sure the IPs are not black listed.
Thank you ! Zero-config fixed the problem.