Hello, my name's Jorge, I am an electronics engineer with experience programming embedded devices.
I have over three years experience working as a freelancer, developing different custom solutions in the fields of IoT, robotics and automation.
I have read the details of your project, I have experience with the technologies needed: Raspbian, Arduino, C. I have worked with MySQL and Json as well. Please let me know more details about the vending machine prototype to see discuss how I might help yoou. I'd be glad to answer any possible questions you may have, in order to start working on your prototype as soon as possible.
Thanks in advance for your time, we could talk in spanish if you wish.