For any app developers, bloggers, or facebook novices out there that are in need of knowing how to find your facebook id after creating a customized url here is a VERY VERY VERY easy link I found to get it:
All you need to do is replace “longislandwebsitedesigner” in the url bar with whatever your customized page link is and press enter.
If you don’t have a customized url then it’s a piece of cake. Just view your page or profile and it will be that long string of numbers at the end of the link.
Ex: https://www.facebook.com/pages/Online-Thrift-Shop-Current-Thrift/505729602798318 <– Thats it