Hi @Shekhar_S, welcome to the community forum 
!
Is there a way to pass protobuf format data to rest endpoints in K6?
As long as you can generate it you can send it as an ArrayBuffer and that will work.
While k6/grpc knows how to format protobuf for itself it does not expose this functionality to anything else, so this is currently not possible natively. There is an open issue which hasn’t been prioritized, and is unlikely to be given our current prioritize.
We are welcoming PRs, but this likely will need some more design so it might not be a great first issue 
A user have reported being able to generate the protobuf message in js only. But I haven’t tested it and it seems to involve multiple steps given previous comments.