undefined: grpc.SupportPackageIsVersion7 grpc.ServiceRegistrar

Already they have provided this solution in their documentation here. I had the same issue and here is my solution:

go get -u github.com/golang/protobuf/{proto,protoc-gen-go}
go get -u google.golang.org/grpc
protoc --go_out=plugins=grpc:. *.proto

Here is the explanation if you are not using Go modules:

The gist of this error is that the version of binary used to generate the code isn't compatible with the current version of code. A quick and easy solution would be to try updating the protoc-gen-go compiler and the gRPC library to the latest version.

go get -u github.com/golang/protobuf/protoc-gen-go

then regen the proto

heres a link to a reddit thread that discusses the issue

I solved this problem by specifying grpc-go version to v1.33.0-dev, but this version is not included in ver v1.31.1.