Error in go.mod file in quickstart google cloud platform file

Hi all,
I am trying to deploy the google cloud function for downlink to google pub sub topic using the go function file shown in this link,, while deploying the function it is showing error in go.mod file that there is a problem in first line of the file i.e. “module iotpubsub”. According to my knowledge this particular line should be some kind of a link. Can anyone guide me what should be the correct go.mod file to be used here