Sendhttppost

Trying to call Web API with SENDHTTPPOST. My API return a table of rows like this
[
{ "value1": 0, "value2": "string", "value3": "2018-11-21T13:42:44.584Z" },
{ "value1": 20, "value2": "HELLO", "value3": "2018-11-21T14:47:24.0376587+01:00" }
]

I got an error during results parsing in SENDHTTPPOST like this one
CODE: ErrorWebServiceCall (#217)

SOURCE: WebServiceExecute

MESSAGE: Error while invoking the web method Send : Exception has been thrown by the target of an invocation. :

System.Web.Services.Protocols.SoapException: An item with the same key has already been added.

at Advantys.Workflow.Applications.SendHttpPost.SendHttpPost.Send(String WFGEN_CONTEXT)

Ho may i solve this ?

Thanks