Error for alerting in Grafana

Trying to set up alerting in Grafana. It worked for a few months and then suddenly it stopped sending alerts to the mail. When I tried to send a test notification to the mail, found errors logged in a log file.

logger=alerting.notifier.email t=2023-01-17T15:20:24.939973555+05:30 level=error msg=“Missing receiver”
logger=alerting.notifier.email t=2023-01-17T15:20:24.940075398+05:30 level=error msg=“Missing group labels”