Hi there, just a quick one this time.
Today I struggled for some time with a Facebook app, which was meant to display as a page tab. A basic functionality: take an external URL and display it within the page tab.
The problem was that the page was not appearing, although the server was publicly available and pasting the URL in a browser worked as expected. After some research, it came out that the URL using commas and semicolons in querystring has to be encoded, otherwise Facebook won’t like it.
Thus, changing from http(s)://www.example.com/page.html?a=1,2&b=3;4
seems to solve the problem and the page gets displayed.
Hope this helps,