trying to invite a facebook friend to a group it says this: 'There was an issue sending your invite. Please try again'. it worked for 2 other friends

its a new private hidden group. clearly user error, but cannot find out how to fix

there are no questions or other things that must be done to 'join'- (no admin assistant setup)the invite link doesnt seem to work either

this is a new group, i added 2 others with the same link, but now cannot seem to add the thirdi did add each person as a facebook friend prior to invite