What you need to find out is how this application handles HTML Forms. You should be able to find out thru the application help. PayPal's item button code is basically an HTML Form. Not all sites or site editors handle HTML Forms in the same manor.
Some sites won't even allow you to use these forms. With some sites, you must be in a specific editing mode. The sites that won't allow forms usually allow text or hyperlinks. If that's the case, you can use the email or hyperlink version of the item button code.
