The zip file produced [here](https://github.com/aws-samples/aws-lambda-extensions/tree/2f7d61e8e66df99eb5fa733ff23bd25ce18b6d26/go-example-lambda-runtime-api-proxy-extension#building-the-package-and-dependencies) and [here](https://github.com/aws-samples/aws-lambda-extensions/blob/2f7d61e8e66df99eb5fa733ff23bd25ce18b6d26/go-example-lambda-runtime-api-proxy-extension/Makefile) includes the `ARTIFACTS_DIR` in the zip making it invalid and the extension does not run. You're probably missing the zip `-j` flag.
