Art. 64 CISG
(1) The seller may declare the contract avoided:
(2) However, in cases where the buyer has paid the price, the seller loses the right to declare the contract avoided unless he does so:
The Secretariat Commentary on Art. 60 of the 1978 New York Draft, predecessor to Art. 64 CISG, gives insight into the drafters' unterstanding on the eve of the 1980 Vienna Diplomatic Conference.
Overview of case law on Art. 64 CISG: UNCITRAL Digest
The UNCITRAL Digest on the CISG can be used as a starting point to discover the relevant case law on this article.