Notice
A formal communication that a contract requires in order to preserve a right — typically the right to claim time or money. A notice is valid only if served by the contract’s method, to the contract’s addressee, within the contract’s time.
Under FIDIC 2017 there is a further requirement that catches competent people: a Notice must identify ITSELF as a Notice and cite the clause under which it is given. An email that describes the problem in full detail, to exactly the right person, comfortably inside the window, is not a notice if it does not say that it is one.
And actual knowledge does not cure a defective notice. The instinct that "they obviously knew" must be a defence is overwhelming, and it is wrong — the courts have been consistent for a very long time, because the whole purpose of the provision is to create certainty that a clock has started. Meritorious claims die on the channel and the addressee, which is a stupid way to lose money and entirely avoidable.