How would you troubleshoot a transactional replication setup where a subscriber has stopped receiving new changes entirely?

You would check the status of the relevant replication agents, such as the log reader agent and distribution agent, in Replication Monitor or through their job history, review any error messages logged, verify network connectivity between the involved servers, and check whether a specific data change caused a replication conflict or error that halted the process entirely.

-- Check the job history for the distribution agent
EXEC sp_help_agent_default;

-- Review recent errors
SELECT * FROM MSrepl_errors ORDER BY time DESC;