1. go to eBay selling manager and please make sure you check this:
2. The reason not everyone is seeing the "Add to cart" button is due to the fact that not all price monitors / listers support adding the ASIN to the custom label(SKU) field.
(We are working on a solution for everyone).
Currently known supported monitors that add ASINs to the Custom label field on eBay:
Web Seller Guru
Dshopit (need to activate):
If you are using Dshopit, go to this link: http://dshopit.com/members/en/pict_params
And choose "Fill ASIN"