Plesk Migration fails: Panel Migrator failed to connect to RPC Agent

Symptoms

• Migration fails with the following error:
  

  PLESK_ERROR: Panel Migrator failed to start RPC Agent on '203.0.113.2' server.
  RPC Agent is required for communication between current server and '203.0.113.2' server

  ---

  PLESK_ERROR: Failed to fetch basic information about resellers, clients and domains data from source servers 
  Cause: unpack requires a string argument of length 4 
  That is a critical error, migration was stopped. 

• RPC Agent is installed and running on the source server.
• It is not possible to connect from target server to source one via telnet utility:

  C:\> telnet <source_server_IP> 10155

  Note: if telnet utility is not installed check the article Install Telnet Client

• On target server  %plesk_dir%var\modules\panel-migrator\sessions\TIME_STAMP\debug.log   has the following error:

  CONFIG_TEXT: PleskConnectionCheckError: Failed to connect to target Plesk server by Plesk API: <urlopen error [Errno 10054] An existing connection was forcibly closed by the remote host>

Cause

Network issue, required port for migration is closed by a firewall.

Resolution

Check network and make sure that is it possible to connect from target server to source one on port 10155.

Additional Information

Migration cannot be started: Panel Migrator failed to install RPC Agent

Migration Guide. Migration Prerequisites