The payment handling fee is our service fee of 3.85% which is applied for all credits earned in the xChange requests. The reason for this service fee is that we credit funds to the wallet on a daily basis, even before/without recovering the payment from the counterpart, taking over the effort of payment collection and risk of late/no payment by the counterpart.
If your account balance is positive, the credits received in your wallet can be immediately used to settle any charges you have on xChange (i.e. container purchase).
If at the end of a given month your wallet balance closes with a positive amount, the positive balance can be paid out to your bank account as explained in this article.