Can not integration with prometheus which installed in k8s

i have one k8s cluster and has added into gitlab,also i have installed prometheus in k8s and works ok;now i want to integration prometheus,so i enter “admin->kubernetes->Intergration” and check “Enable Prometheus integration”,then “save changes”,when i goto “Health” tag,it show " Connection failed We couldn’t reach the Prometheus server. Either the server no longer exists or the configuration details need updating"。my gitlab version is 14.0.0,prometheus is deploymented in “gitlab-managed-apps” namespace and service name is “prometheus-prometheus-server”。
how can i do?