An act performed by a representative without authority or in excess of his authority is unenforceable against the principal, unless the contracting third party legitimately believed in the reality of the representative’s authority, in particular because of the principal’s conduct or statements.
Where he was unaware that the act was performed by a representative without authority or beyond his powers, the contracting third party may invoke its nullity.
Neither the unenforceability nor the nullity of the act may be invoked once the principal has ratified it.