I recommend to contact a lawyer [friend or family] because you should check many private details. One question is if the code is yours. In intellectual propert

I recommend to contact a lawyer [friend or family] because you should check many private details. One question is if the code is yours. In intellectual property it is yours as an author but that does not mean your customer could not have rights depending on the written or tacit agreement. If I were you I would be prepared for that conversation with a legal professional and not continue the discussion with your customer about this topic until things are crystal clear. I also recomment to post in sites as https://law.stackexchange.com/ https://law.stackexchange.com/ and Reddit.