Solutions which can be checked:
Let's use the following example: Guest's birthday is in April. They also signed up on the app in April.
If a guest signs up for the app during the month of their birthday, they will not receive the birthday campaign. This is based on the "Should the above reward be given in the month of sign up?" flag on page 2 of any campaign, it may differ as well.
If this flag is not checked, guests who signed up for the app in April with a birthday in April will not receive the birthday reward.