Add invoices which contain personal data in the recipient address and must be stored for 10 years safe from manipulation (and then deleted). Combine that with a

Add invoices which contain personal data in the recipient address and must be stored for 10 years safe from manipulation (and then deleted). Combine that with a deletion request, and now you need to delete some data about a customer and keep the rest, which is pretty annoying (yay referential integrity), especially if you're changing existing software, and don't develop from scratch. Of course for the data you can't delete, you now have to restrict access as much as possible, so for every feature in your software you have to figure out if it should use the censored or full data. Then you have to figure out how much of the order history (up/downgrades etc.) you need to keep so you can keep track of who changed what in case of disputes, etc. You need to keep track of payments and invoices for accounting and tax purposes, and of course accounting records must be immutable. Then write documentation describing all the ways you process data and ensure you have a valid updated data privacy contract with all your service providers.