1👍
✅
Try placing single quotes around {{friend.uid}}
onclick="FacebookInviteOneFriend('{{friend.uid}}');"
Also try adding a debug statement to your function to see what, if any, value is being passed:
function FacebookInviteOneFriend(UserId) {
alert(UserId);
FB.ui({
method: 'apprequests',
message: 'My message'
to: UserId
});
}
Source:stackexchange.com