Unable to upload an artifact using REST API

I'm trying to add a new artifact to an existent asset by calling the REST API.

The URL I use for the POST request is:
https://<server_IP>:9446/ram.ws/internal/assets/AAAAA-BBBBB-CCCCC-DDDDD/1.0
I add the following headers to the POST request:
Content-Type: application/java-archive   (I tried many other combinations)
oslc_asset.name: TestProject.zip (This is the name that should appear in the asset)

The binary file is attached to the body as "application/zip" content.

When I run the POST command I get the following error:
...
  <oslc:statusCode>500</oslc:statusCode>
    <oslc:message>Error POSTing asset null : Failed parsing JSON source: java.io.StringReader@62816281 to Json</oslc:message>
    <ram:trace>
        <ram:className>com.ibm.ram.repository.rest.RestAssetsService</ram:className>
        <ram:fileName>doPost</ram:fileName>
        <ram:lineNumber>1125</ram:lineNumber>
        <ram:methodName>RestAssetsService.java</ram:methodName>
        <ram:nativeMethod>false</ram:nativeMethod>
    </ram:trace>
....
Any idea about what can I do wrong? I don't understand why it tries to interpret the content as Json...

Thank you