A Domain Model can only be validated by a Business User

Since the Domain Model represents the problem space of the business, it can only be vetted and validated by a Business user. A Product Owner can stand in as a replacement for the business user, but they will eventually need to seek consensus on the model.

It is vital to get the model to represent the business processes as closely as possible. If you get the model right, your software delivers value to the end-user. If the model is wrong, your software becomes an obstacle to work around.

Because non-technical users are involved, a visual representation of the domain model works best for collaboration and concensus.

Still, a model in code should be verifiable by business people as well, as long as they can recognize domain elements and can read code. Ultimately, your software codebase is the absolute source of truth.