Its probably a security thing on your site blocking the .php request.
Can you add just some plain text to a HTML Widget in its place so we can test that the side bar is working first. If it is we will need to look at why your code ins’t working
Super late response but I still haven’t figured this out. I added some plain text and this showed up. I also tried to add the HTML code to a normal blog post to see if the sidebar was the problem but this wasn’t the case, the banner still didn’t show up. Is there something wrong with the code or could it be a security issue?