Command
rs.reconfig( { _id : "rs", members: [ { _id : 0, host : "..." }, { _id : 1, host : "..." }, ] } )
Error:
"errmsg" : "Missing expected field \"protocolVersion\"" "code" : 93 "codeName" : "InvalidReplicaSetConfig",
However, https://docs.mongodb.com/manual/reference/replica-configuration/#rsconf.protocolVersion documents a default value of 1 for this field.