Thats just the standard code. It is not indicative of the error. If your browser rejected iframes you would see that message directly on the kiwitrees page
You need to find your web server error log files to see the full details of the 500 error message.
However, I do note that your manuel jose site (the one I am looking at for this issue) is still on PHP 8.0.16. Try putting it back to 7.4.
