Amazon MWS API with R

Hello,

I am trying to get data from Amazon MWS API using GetMatchingProductForId operation. When I use Amazon MWS Scratchpad it works perfectly fine.

I am now trying to replicate the urls that are sent in the HTTP POST request but I get a Signature error message. I need to understand how the url request should be structured.

Below is the detail of the request in Amazon MWS Scratchpad, I ANONYMIZED private identifiers but that is the only thing I changed:

HTTP POST

POST /Products/2011-10-01?AWSAccessKeyId=ANONYMIZED
&Action=GetMatchingProductForId
&SellerId=ANONYMIZED
&SignatureVersion=2
&Timestamp=2018-09-28T05%3A45%3A43Z
&Version=2011-10-01
&Signature=ANONYMIZED
&SignatureMethod=HmacSHA256
&MarketplaceId=A13V1IB3VIYZZH
&IdType=EAN
&IdList.Id.1=9781933988665 HTTP/1.1
Host: mws.amazonservices.fr
x-amazon-user-agent: AmazonJavascriptScratchpad/1.0 (Language=Javascript)
Content-Type: text/xml

String to Sign

POST
mws.amazonservices.fr
/Products/2011-10-01
AWSAccessKeyId=ANONYMIZED&Action=GetMatchingProductForId&IdList.Id.1=9781933988665&IdType=EAN&MarketplaceId=A13V1IB3VIYZZH&SellerId=ANONYMIZED&SignatureMethod=HmacSHA256&SignatureVersion=2&Timestamp=2018-09-28T05%3A45%3A43Z&Version=2011-10-01

=======

Now my question is, (and let's imagine my signature was created correctly), from the HTTP POST, what should the request look like ? Here is my attempt:

https://mws.amazonservices.fr/Products/2011-10-01?AWSAccessKeyId=ANONYMIZED&Action=GetMatchingProductForId&SellerId=ANONYMIZED&SignatureVersion=2&Timestamp=2018-09-28T05%3A52%3A33Z&Version=2011-10-01&Signature=ANONYMIZED&SignatureMethod=HmacSHA256&MarketplaceId=A13V1IB3VIYZZH&IdType=EAN&IdList.Id.1=9781933988665

But what about '\n' escape characters that are in the scratchpad ? and what about 'HTTP/1.1' at the end, should I include that also ?

Thanks for your help.