Symfony Framework and Atlassian Connect

I’m trying to develop a plugin with PHP with Symfony. Everything seems to work correctly, the plugin is installed and creates a jiraIssueTabPanels correctly inside the issue view named “SW Tab” but when i try to fill the content with a http call that return html i have an error as you can see in the attachment. The response is a plain/html response. I can’t see any logs and i can’t see any error on jira cloud instance. The REST call to Cloud works.

I’ve included this on the html page and all works:

<head><script src="" type="text/javascript" data-options="sizeToParent: true;"></script></head>