There could be several reasons why your cashback cannot be withdrawn:

1) The maximum number of withdrawals for this month has been reached, or it is currently not within the withdrawal period: Each promoter can initiate one cashback withdrawal per month, and the withdrawal can be done on Wednesdays
2) Your available balance has not reached the minimum withdrawal amount: The minimum withdrawal amount for commissions is $10, and the maximum withdrawal amount per transaction is $1000
3) Pending settlement cashback cannot be withdrawn. The withdrawal amount should be equal to or less than the available balance