SellerExpress uses the product barcode to request ASINs from Amazon, this however may not get ASINs for all of your stock. In some cases your barcode may not return an ASIN as it may differ to what Amazon uses. If a product doesn't list you'll need to manually add the ASIN or Amazon barcode to your product to get it to list.
How do I find out which products don't have ASINs?
To create a list of which products have ASINs and edit them in bulk go to the 'Reports' screen and generate an 'Advanced Stock Import File' for 'All Suppliers'. Before you hit 'Generate' make sure to tick 'Listing IDs / ASIN's'. This will list all known ASINs for products in your report.
Once the report is generated open it and find the products without ASINs listed. Add the correct ASINs and Import the file back into SellerExpress. For more information on 'Advanced Imports' click here.
If there is only the one product?
If a single product listed on Amazon does not match the product you added in SellerExpress, search for the product on the Amazon marketplace you're having the issue with and get the ASIN for that product. You can get it from the products URL.
You can manually set the ASIN for any product by inserting the ASIN into the 'Listing ID' field on the 'Marketplace' tab of the 'Product Screen'.
NB: ASINs may differ per Amazon marketplace.