It's impossible to add the app on Facebook

I spent almost 5 hours trying to add the app on Facebook. Please HELP ME!

When I click Choose Facebook Page Facebook open a window which says An error occurred. Please try again later.

I tried to add funpage ID number, but absolutely same message. 

Tried to do that from another facebook account, same message absolutely.
Are you sure this link is correct? Please check and help.

Thank you!