1st thing to check, have you set the birthday channel.
If not the bot has no idea where to wish you a happy birthday and will not send it. Use
/channel <#channel> to set that channel.
2nd, has that user set their birthday?
Have the user run
/getbday and if the bot responds with "You have not set your birthday yet." Look at Commands to do so.
All birthdays will be announced at 12:00 noon in UTC. Once you set your birthday in one server with the Birthday Bot it will be announced in all servers the bot and you share.