api gateway trying to use method.request.body in URL Path Parameters

Question

Created a api gateway to s3 directory service, and everything is working 
I am trying to use method.request.body..$.cust in the URL Path Parameters to extract the request body info as a s3 destination. The request body is as below, 
{"cust" : "cust123"} 
Also tried method.request.body..$['cust']
and method.request.body..$.cust

Tried various different ways including but it doesn't seem to recognize the method.request.body, i tried to use the following links, 
https://docs.aws.amazon.com/apigateway/latest/developerguide/request-response-data-mappings.html
https://docs.hevodata.com/sources/engg-analytics/streaming/rest-api/writing-jsonpath-expressions/
http://jsonpath.com/

Answer

This is doable using an API Gateway Request Mapping Template.  First, I've made some assumptions:
* You have a POST or PUT API method with a Request Body json payload something like this: {"cust" : "cust123"}
* In your Integration Request you are making a direct integration call to S3 to GET an object with a Path override that has a path parameter ending with or containing "/{cust}"

If so, add the following Request Mapping Template:

```
#set($body-json = $util.parseJson($input.json('$')))
#set($context.requestOverride.path.cust = $body-json.cust)
```

Answer

I tried this and got

Method request body before transformations: [Binary Data]
Execution failed due to configuration error: Cannot map binary data to parameters

And I have these set in the settings like below, 
![Enter image description here](/media/postImages/original/IModr9UiAdSpik2dtogUis9Q)

![Enter image description here](/media/postImages/original/IMlIKjZhUSTD6XhRGgBwBsog)

![Enter image description here](/media/postImages/original/IMcDLRxMJ8SUalIbibnwYrAg)

api gateway trying to use method.request.body in URL Path Parameters

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