For calculating the billable amount an on-board unit (OBU) needs to be installed inside the vehicle.
The OBU records kilometres driven on tolled roads, transmits the data to the MYTO system and the toll charges are then deducted from the prepaid credit or billed to the registered bank account (postpaid), all automatically.
The prepaid credit can usually be topped up via Credit/debit card or Bank transfer. Please note that a bank transfer could take several days.
Related articles:
MYTO Mobile App (Czech authority)
How is the MYTO CZ calculated?