Breach of contract (Global)

Hello, I have a question from BPP kit. Lise, a wholesaler from S., entered into a contract with Pascal, a manufacturer from P. to supply her with machinery that was to be built according to her specific design. Several months into Pascal's build process, Lise decided that she did not require the machines after all, and notified Pascal of her intention not to pay fort he machines. You should assume that UN Convention on Contracts for International Sale of Goods applies. This is an anticipatory breach. When would it be a breach during performance in this case? I appreciate any help that you can provide.