You may not have given permission for Facebook to share your email address with LeagueRepublic and Facebook have provided the following possible reasons for this...
1/ Permission not given for the LR app to receive email address (within FB --> settings --> apps --> LeagueRepublic)
2/ No Email address on account
3/ No confirmed email address on account
4/ No verified email address on account
5/ User entered a security checkpoint which required them to reconfirm their email address and they have not yet done so
6/ Users's email address is unreachable