Mongodb start a local sharded cluster - mongodb

Question

Trying to set up a local sharded cluster for testing (mongo 3.6). There are a number of scripts online (e.g here, here) all of which seem to fail for me.
running (cribbed mostly from the 2nd example above):
start the config server:
mongod --configsvr --replSet csrs --dbpath /data/db/configdb --port 27018 --fork --logpath log/mongods.log
initiate the replica set on the config:
mongo localhost:27018 << !
rs.initiate({_id: "csrs", configsvr: true, members: [{_id: 0, host: "${local_ip}:27018"}]});
!
start the mongod processes:
mongod --port 27030 --dbpath /data/db/db1-0 --shardsvr --replSet rs --fork --logpath log/mongod1-0.log
mongod --port 27040 --dbpath /data/db/db2-0 --shardsvr --replSet rs --fork --logpath log/mongod2-0.log
mongod --port 27020 --dbpath /data/db/db0-0 --shardsvr --replSet rs --fork --logpath log/mongod0-0.log
initiate the replica set(s)
mongo localhost:27020 << !
rs.initiate({_id: "rs", members: [{_id: 0, host: "${local_ip}:27020"}, {_id: 1, host: "${local_ip}:27030"}, {_id: 1, host: "${local_ip}:27040"}]});
!
(note, initial script had a separate rs for each shard, which caused the same error)
start a mongos and point it to the config server:
mongos --configdb csrs/${local_ip}:27018 --port 27017 --fork --logpath log/mongos.log
log into the mongos and add shards:
e.g. sh.addShard("rs/${local_ip}:27020").
This last step is where this goes wrong, getting the error
"errmsg" : "Could not find host matching read preference { mode: \"primary\" } for set rs",
"code" : 133,
Can anyone provide any pointers on what I'm missing here?