Build a embedded RFID card system device for payment transactions - PCB design, software & Product design

Multiple devices will be used in one setup (1 to +100 devices). They authenticate to the network and receive a unique ID. Use of esp32 or another uc for wifi connection to central server. Creation of server software api to communicate with all devices. API talks to an existing MSSQL database with all information about pricing, customers, ... Need to register new devices. This will assign an id to it and define the pricing that it should use for the transactions. Prices that a device is using are centrally managed and can be changed. This information is sent from the server to the device. Users can use an rfid card to pay and to start a transaction. (using relais output or serial communication) The card stores the amount of money that still can be used. With every transaction, the amount is updated on the card and will sync to the central MSSQL database on the server. If the device was unable to send the transaction to the server, it will store the transaction on the card for later synchronisation State information about the transaction is displayed on an lcd We want to have as much logging as possible about all the transactions going on. For this reason, devices send log information to the server. If they are not able to do this, logs will be stored locally in flash (with log rotation in case flash gets full) for later upload. Devices register transaction and log data with the correct time information. For this reason, devices are able to sync their internal clock with the server. Possibility to fix issues in the firmware and optionally add new features in the future without having to remove the microcontroller from every device. For this reason, devices support over-the-air upgrades. RFID cards are formatted Mifare cards with changed keys. Cards are preformatted and a unique ID is stored so no other cards can be used. Money will be added to the cards using an external payment device (money stored on card and in MSSQL customers table ) - this is not part of this job