Resilio Connect Management Console uses bootstrap token to authenticate new agents and allow connection. The token is pasted to agent's config file and delivered to an agent.
When an Agent connects to MC for the first time, it sends the bootstrap token from its config. If the token matches (together with certificate fingerprint), agent is allowed to connect. Management Console generates a unique client_token for this agent. Agent saves the client_token in its settings and uses it for further connection to MC.
Bootstrap Token expiration
For security reasons bootstrap token has expiration date. You can change it in MC ->Settings tab, but it's advisable not to set a too long period.
When token expires, MC gives message "No valid token", and new one is to be generated so that new Agents can connect. The Agents that are already connected will not be affected - they will be using the client_token.
You can also re-generate the token if there's suspicion that it got compromised. Again, the currently connected Agents will not be affected as they'll be using client_token for connection.
If one of the current Agent gets its settings deleted (reinstallation, for example), it is to get new agent config with new bootstrap token and certificate fingerprint.