I am investigating using CosmosDB (previously DocumentDB), we currently use MongoDB so I am trying to use the MongoAPI for CosmosDB.

I have created a CosmosDB deployment in azure, created a collection and specified a partition key of "/rateId".

As far as I can understand from [Microsofts documentation](https://learn.microsoft.com/en-us/azure/cosmos-db/documentdb-partition-data#partition-keys) this partition key should relate to a property in each document I insert, so I am trying to insert a basic document like so:

```
{
    "rateId": "test.1",
    "val": "test2"
}

```

However when I try to insert this (through Mongo C# driver or through MongoChef) I get an error "document does not contain shard key".

[![enter image description here](https://i.stack.imgur.com/wF0ze.png)](https://i.stack.imgur.com/wF0ze.png)

I have tried this every which way I can think of and every time I am denied with this error. Am I misunderstanding how this is meant to work, or doing something wrong?