Is there a fee for using the service
No, all sections don’t have any fee, except Crypto.Exchanger. Each party of mutual exchange has to pay the fee of the selected payment system on their own. For example, a seller of WMZ pays the WMT commission (A fee for provision of informational and technological interaction between correspondents in the WMT system is charged for each transaction and makes 0.8% (not less than 0.01WM*) of the amount of payment).
The exception is Crypto.Exchanger section. There a cryptocurrency seller pays 0,1% of the amount of a payment.