"parameterOverrides" in pre-provisioning hook response not working

Question

Hello,  
  
I'm trying to follow the instructions in https://docs.aws.amazon.com/iot/latest/developerguide/provision-wo-cert.html  
  
In there it mentions the "parameterOverrides" option that sends values back to the device during provisioning.  
  
However, using the code in https://github.com/aws-samples/aws-iot-fleet-provisioning, the response from RegisterThing always comes back as
 `{'deviceConfiguration': {}, 'thingName': 'MyNewThingName'}`
, i.e with an empty deviceConfiguration.  
  
Example of lambda handler in simplest form that fails:

```
def lambda_handler(event, context):
    return {
        "allowProvisioning": True,
        "parameterOverrides" : {
           "customKeysAndValues": "sentToDevice"
        }
    }
```

Is there anything I'm missing here?

Answer

Glad it worked. Yes, we are working on fixing the documentation. Thanks for pointing it out.  
  
Thanks,  
Ranga

Answer

Thanks for reaching out. If you are using the sample template from Github README, it says DeviceConfiguration is empty. (very end of README. file)

```
"DeviceConfiguration": {}
```

If you are planning on sending data back to the device, you need to define DeviceConfiguration parameters. The values can be provided by the Lambda function. For example, I would like to send `ServerUrl` to device, then I define something like,

```
    "DeviceConfiguration": {
        "ServerUrl": {"Ref": "ServerUrl"}
    }
```

My Lambda function will return the value for ServerUrl through parameterOverrides.

```
def lambda_handler(event, context):
    return {
        "allowProvisioning": True,
        "parameterOverrides" : {
           "ServerUrl": "https://amazon.com/devices" // dummy URL
        }
    }
```

Lambda function does supply the values for the parameters you defined in DeviceConfiguration. This way, customer knows what parameters are going to device by looking at the provisioning template.  
  
Hope this helps,  
Ranga

Answer

Great! It now works :)  
One thing that could be improved in the docs as a follow-up is having in the examples something like a you described to reference "Parameter" values, i.e. having

```
"DeviceConfiguration": {
    "SomeConfig": {"Ref": "SomeParameter"}
}
```

Because from my side I interpreted (wrongly) that simply adding something to "parameterOverrides" would already add to "deviceConfiguration" configuration. At least from this quote in the doc:  
_"parameterOverrides" will be added to "deviceConfiguration" parameter in RegisterThing response payload._  
  
Nevertheless, your answer solved my issue, thank you very much!

"parameterOverrides" in pre-provisioning hook response not working

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