I am mostly an embedded/Linux driver engineer, but I think I know the basics of HTTP, REST APIs, Docker containers, how the web works overall etc.
But, like. What are we doing?
What do you mean make the billing backendless? Obviously there has to be a backend to process the payment. What are you even saying? You are presumably not building a distributed blockchain - and even that requires permanent nodes.
Same with serverless (which are just Edge Functions and could just be called that, or serviceless, if you really wanted to define it negatively).
If these people named NoSQL, it would be called databaseless.