Elppa Inc. is a calendar year, accrual method C corporation. In December 2016, Elppa enters into a contract with XYZ pursuant to which Elppa pays XYZ $200,000, and XYZ is required to renovate Elppas parking lot by the end of 2017. In May 2017, XYZ commences renovating the parking lot, and in July 2017, the renovation is completed. When does economic performance occur? When can Elppa deduct the $200,000 payment?