Error :

The server network address “TCP://SQL Server:5022” cannot be reached or does not exist.
Check the network address name and that the ports for the local and remote endpoints are operational.
(Microsoft SQL Server, Error: 1418)

To over come the issue follow the below steps.

Drop the Mirroring Endpoints from Principal and Secondary.

select * from sys.database_mirroring_endpoints 
GO
DROP ENDPOINT EndpointName

Create Mirroring Endpoint Principal and Secondary.

CREATE ENDPOINT [Hadr_endpoint] 
  STATE=STARTED
  AS TCP (LISTENER_PORT = 5022, LISTENER_IP = ALL)
  FOR DATA_MIRRORING (ROLE = ALL, AUTHENTICATION = WINDOWS NEGOTIATE
, ENCRYPTION = REQUIRED ALGORITHM AES)
GO

GRANT Connect Permission no Endpoint  to SQL Server Service Account

GO
GRANT CONNECT on ENDPOINT::Hadr_endpoint TO [Domain\AccountName];
GO