There are few reasons why this can happen.
First of all ensure that you have earned the minimum amount. You need to have earned a minimum of $10 before you can register / login for a Payoneer account.
It could also be possible that your Payoneer account is already associated with another account on AdF.ly. It is against our Terms and Conditions to have multiple accounts, please see:
If you are trying to link a new Payoneer account to your AdF.ly account, please ensure that you have completed the process to remove your old Payoneer account. Please see:
If you are unable to login to your Payoneer account, please contact Payoneer Customer Support department.
If this does not help you to solve the problem, please contact us.