What are the charges if a direct debit is rejected?

The direct debit rejection fee is €10 per rejected payment. 

This can happen if your account balance does not allow you to pay a bill by direct debit. 
For example, if your Internet service provider charges €30 for your box every 05th of the month, and your account balance is €20 at the time of debiting.

If, at the time of debiting, your balance is less than the amount of the fees you owe, Nickel will debit part of the fees (i.e. the amount of your balance) and then the remaining amount as soon as your account is funded. 

For example: if you owe €10 in rejection fees but your balance is €7, Nickel will deduct €7 in partial fees. You will still owe Nickel €3, which will be deducted thereafter.