Vault Agent Injector is not able to intercept pod

I have followed this article and able to achived the result in my one GKE cluster but not able to inject secret in my another GKE cluster. Both cluster has same firewall rule.
Can someone help what is the starting point to debug.?
which pod I should look to troubleshoot.

Basically the Vault injector agent is not able to create sidecar agent and init container in my deployment object. I have given the annotation correctly.