Create a comment with custom properties via Java API

I want to create a comment with custom properties via the Confluence Java API (in a Rest endpoint I am exposing by a Confluence plugin).

My code is as following:

        Content commentedPage = contentService.find(new Expansion("id"))

        comment.getProperties().put("highlight", comment.getHighlight());
        comment.getProperties().put("coordinates", comment.getCoordinates());

        String amdocsProps = "{\"key\": \"amdocsProps\", \"value\":" + new Gson().toJson(comment.getProperties()) + "}";
        logger.error("amdocsProps is: " + amdocsProps);

        Content.ContentBuilder contentBuilder = Content.builder()
                .body(comment.getContent(), ContentRepresentation.STORAGE)
                .metadata(new HashMap<String,Object>(){{put("properties",new HashMap<String,String>(){{put("amdocsProps", amdocsProps);}});}});

I printed to the log the value of amdocsProps and it is as following:
{“key”: “amdocsProps”, “value”:{“visibility”:“medium”,“priority”:“medium”,“reply”:,“highlight”:{“text”:“performed during customer billing and f”,“occurrences”:1,“occurrence”:1},“coordinates”:{“pageObjects”:[{“pageId”:28216445,“pageVersion”:1}],“section”:“overviewsec”}}}

When I take this json string and use it as the body of Confluence API - /rest/api/content/{commentId}/property - The custom properties are added as required.

But, when doing it via server side - the properties do not get added.

I’ve tried also to create the comment without the properties, and only after the creation, to fetch it and add to it the properties. I did it like this:

        Content newComment = contentService.create(;

        @Nullable ContentEntityObject createdComment = contentEntityManager.getById(newComment.getId().asLong());
        ContentProperties commentProperties = createdComment.getProperties();
        propertyManager.setStringProperty(createdComment, "amdocsProps", new Gson().toJson(comment.getProperties()));

But again - the properties do not get added.

What am I doing wrong?
Any advice?