Unpaid customers see a payment page instead of losing the connection
Per RADIUS router: blocked or expired PPPoE customers get an address from the router's Unauthorised pool and DHCP customers keep theirs. Any web page they open says the service is paused, with a link to pay in the portal; their CPE stays reachable from your network, and paying, unblocking or renewing restores the service at once. Router commands for RouterOS 6 and 7 are on the router page.