How can retailers comply with the new law?

Retailers must ensure that not every single sale can be changed after it has been entered into the system. While this sounds pretty simple, it really means that the POS software they use needs to be updated to ensure that inputs can't be changed or deleted. This also means that any change in a sale, whether it is an error or a return, must be entered into the system as a new transaction. In principle, it should be impossible for anyone to change an already saved transaction.

How can a retailer prove that their software is compliant?

There are two ways a retailer can demonstrate that their POS software complies with the new law. They can show the tax authorities that they have a certificate of conformity managed by their software vendor, or a certificate issued by a third-party certification authority.