You may see following status for the computer in Veeam Availability Console -> "Discovery" -> "Discovered Computers":
If you login to the computer in question, launch C:\Program Files\Veeam\Availability Console\CommunicationAgent\Veeam.MBP.AgentConfigurator.exe, double click on VAC icon in the system tray and you will see following:
[ERROR ] 1352 [__42] Veeam.SPP.Agent.ClientAgent: Agent can't pass registration. Reconnecting...
[ERROR ] 344 [__60] Veeam.SPP.AgentManagement.AgentManager: Failed to register agent VEEAM, with id <ID> : Veeam.SPP.Utilities.Exceptions.AgentHasBeenRejectedException: The VAC Agent has been rejected
at Veeam.SPP.AgentManagement.AgentManager.SaveAgent(UserNode user, Guid agentId, AgentInfo agentInfo)
at Veeam.SPP.AgentManagement.AgentManager.RegisterAgent(UserNode user, Guid agentId, AgentInfo agentInfo)
Follow VAC UI > "Discovery" > "Discovered Computers", select computer in question, press "Change settings…" and turn on "Accept new connections"