Interest is paid as long as the following conditions are met:

Interest is paid on the first day of each month based on the balance at midnight - if you moved money into the pot on the 1st of the month, interest won't be calculated until the end of the month

The interest rate is calculated yearly not monthly so if the balance of the pot is still small and you have applied a low interest rate, the interest accrued may not be be a whole number.

Interest is only paid on whole number this means that we can't add a fractional value to the balance, if your monthly interest is less than 1p (1 cent etc) then interest will not be added.