WebHook using anonymous Web Service

Hi Colleagues! How are you?

I'm trying to develop a kind of webhook on Creatio. To achieve it I have created an anonymous web service. The issue I'm experiencing is a Bad Request 400 when receiving the request that is going to be sent by third party app. They are going to send an XML using  POST request, Content-Type = text/xml, and XML Body similar to this one:

<?xml version="1.0" encoding="ISO-8859-1"?>

If i change the encoding for example to UTF-8 it works.

I tried a lot of alternatives but always I get the same result:

1. Changing the service contract,
2. Operation contract,
3. Mapping a custom class,
4. Override WebContentTypeMapper

Any recommendation? Any workaround?

Appreciate it!

Regards.