Get an example of a product that you would like to see for the specific search.
You need this product ID. To check the product ID in Shopify, go to the product page, add .json to the URL, and see the product ID. In BigCommerce, the Product ID is the exact name of the product, unless you have changed it for something else.
Check the product in “How Fast Simon Sees Your Product”.
Check that the searched keyword is indeed found in the product fields.
Make sure that the field is indexed in Settings-> Sync options.
If the searched term is an SKU or a part of the SKU, check that the SKU field is indexed and the searched term matches the SKU.
If the product Is Sellable is false, check out-of-stock settings (Search Results-> Advanced Configuration) Setting is “Hide” - the product is not shown correctly.
Check that you don’t have antonyms for the words in the search terms.