You export your products and you get an error message like this one: Products having a missing reference, Products Identifiers: [2/7, 2/8, 2/9, 2/10, 2/11, 2/12, 3/13, 3/14, 3/15, 4/16, 4/17, 4/18, 4/43, 4/44, 4/45, 5/19, 5/20, 5/21, 5/22, 5/23, 5/24, 5/25, 5/26, 5/27, 5/28, 5/29, 5/30, 6/31, 6/32, 6/33, 6/40, 6/41, 6/42, 7/34, 7/35, […]