Abstract: A transaction device for an owner's terminal for preparing transactions between the owner and a service provider, configured to execute a computer program to calculate a transaction amount for this service, and to generate a message regarding the transaction amount, and an output interface configured to provide this message to the owner. Also described is an intelligent contract for preparing and/or executing transactions between an owner of a terminal and a service provider, a method for preparing such a transaction in a blockchain-based computer network, a computer program product for executing this method, a terminal that has a transaction device, a transaction system for an owner's terminal for executing transactions between the owner and a service provider, a method for an owner's terminal for executing transactions between the owner and a service provider on a blockchain-based computer network, and a computer program product for executing this method.