GRPC: connection reset by peer

Setup:
Kubernetes on Azure
when adding a new network server in the application, on save this error gets thrown.

rpc error: code = Unknown desc = write tcp X.X.X.X:35750->X.X.X.X:5432: write: connection reset by peer (code: 2)

Port 5432 is the PostgreSQL port. Firewall or permission issue?