Hi. I have also the same question and wonder if this is solved?
I have created a Logic Apps Custom Connector in azure, SOAP to REST using WSDL file. The custom connector connects using on-prem GW. I also get error messages back when I use wrong parameters/variables. When I use correct variables the Custom Connector returns : "
BadRequest. Http request failed: the content was not a valid JSON. Error while parsing JSON: 'After parsing a value an unexpected character was encountered"
Using SOAP locally i see the payload like this:
<Interface><![CDATA[<?xml version="1.0" encoding="utf-8"?>.....]]</Interface>
I guess the "![CDATA[" is the reason for the fault.
I have tried a lot of things without success. Very thankful for any help on this issue.