Terraform + GCP NEG Configuration

I have a Google Kubernetes Engine cluster fronted by a HTTP(S) load balancer and I am trying to wire its traffic through a Network Endpoint Group created and managed in Terraform. The NEG refuses to bind correctly to the backend service, so I need a Terraform-experienced GCP engineer to look at the configuration with me over a live screen-sharing session, spot the root cause, and guide me to a clean fix that I can commit to my repo.

During the call you will see:
• my current Terraform modules for the load balancer, backend service and NEG
• existing IAM, subnet and firewall settings that might interfere with attachment
• the error messages returned by gcloud and the console when I apply

What I’d like back from you at the end:
• corrected Terraform snippets (or a minimal new module) that produce a healthy, serving NEG
• a brief write-up of any required GCP console actions or kubectl annotations so I can reproduce the setup from scratch

Please include a short, detailed proposal describing how you would approach the troubleshooting, the checkpoints you expect to hit, and an estimate of how long the hands-on session plus follow-up notes will take. You will be helping me via screen sharing. Live collaboration is essential, so indicate your general availability for a screen-share.