Problems with running Mongodb River for ES

I am running exactly as you did
curl -XPUT 'http://localhost:9200/_river/test/_meta' -d '{
"type": "mongodb",
"mongodb": {
"db": "test",
"collection": "es_test"
},
"index": {
"name": "mongoindex",
"type": "es_test"
}
}'
However I am getting the following exception again and again:

{"error":"MapperParsingException[Failed to parse]; nested:
JsonParseException[Un
expected character ('m' (code 109)): expected a valid value (number,
String, array, object, 'true', 'false' or 'null')\n at [Source:
[B@61f133ea; line: 1, column:8]]; ","status":400}

can you please point out what I am doing wrong? I am completely new to
ElasticSearch and will appreciate your assistance.