Error with prometheus alert rule to grafana using loki as datasource

Question

I'm trying to filter the dev-fluentbit namespace with the line filter which contains "overlimit" and below is my alert rule and i validated that the query in the expression returns data inside Prometheus portal. When i apply this rule i'm getting below error:

one or more objects failed to apply, reason: admission webhook "prometheusrulemutate.monitoring.coreos.com" denied the request: Rules are not valid. Retrying attempt #3 at 1:35AM.

     additionalPrometheusRulesMap:
        rule-name:
          groups:
            - name: FluentbitAlerts
              rules:
                - alert: MemoryBufferOverlimit
                  expr: 'rate({namespace="dev-fluentbit"} |= `overlimit` [30m]) > 0.01'
                  labels:
                    severity: Warning
                  for: 5m
                  annotations:
                    summary: High rate of events with overlimit label
                    description: "The rate of events with overlimit label"