Graphql dynamic input variables issue

[sudheerj]

When I tried to add dynamic input for the root query in these examples I can always see an error "Must provide an operation" message.This occurred only in this examples.

query RootQuery($filter:String) {
accounts(filter:$filter){
account_number,
account_type_code,
region
}
}

Can you please add any example for this kind of requirement.