This Bot Get users Birthdays from a google spreadsheet and send HBD to a group which user are a member of.\
This is due to telegram limitaion to get members of group or channel.
And we can not resolve a user UserName to Unique Telegram id. (to work around it) normal way require for each member to interact with BOT.
BUT there is a way to resolve user id via 3rd party plugin which is build on something that is depricated. (hope it contiue to work.)