what should we check if failure of a terminal, MCU, or recording server to register with the GK or SIP server?

we need to check the below:-

1. The network is disconnected. 

2. The operating system on the GK or SIP server enables the firewall, or the registration port (1719 for H.323, or 5060 for SIP) is blocked.

3. The GK or SIP server rejects the registration because registration information is different from the preset information.

4.  Licenses are insufficient. 

5. A number conflict occurs. 

6. The GK service is offline. 

7. The versions do not match.