For IRS purposes, the donation or purchase is made when the money leaves your control and is no longer cancellable or retrievable. If the entire purchase was finalized on 12/31 and you could not have canceled the delayed items, then it would be a 2025 donation, even though the charity did not receive the items until 2026. However, if parts of the order were cancelable by you (even if you didn't realize it), then those portions were not donated until 2026.
