gRPC building instructions

The first thing you need is Protocol Buffer Compiler Installation.
Then install go plugins for the protocol compiler:

go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest

Now you can rebuild this with the following command:

protoc --go_out=. --go_opt=paths=source_relative --go-grpc_out=. --go-grpc_opt=paths=source_relative sum.proto