help with product identifiers

[rockz1101]

I sell crystals ..no two alike.. ebay wants product identifers. I see no help in the product catalog and eBay says "exact". 

Are we in this category,  supposed to make up SKU numbers? 

Help is appreciated, Thanks!

[lovefindingtreasures2]

Being collectibles, no SKU required as far as I have found. It's hard for our category 😞