This problem may be caused by two reasons:
1. Your product is already present in the other Listings.
When adding Magento Products to your M2E Pro Listing, you will see the Advanced Filter on top of the page. There is an option that allows you to show or hide products present in other Listings.
Most probably, it is set to Yes, so Magento Products, which are added to other Listings, are not displayed in the search result.
Make sure to set the Hide Products presented in other M2E Pro Listings option to No, and click on the Search button. As a result, the needed product will be displayed in the grid.
2. The product is not added to the Website associated with Listing Store View.
A website contains one or several Store Views. You need to choose the appropriate Website when adding a new Product to the Listing. However, if the Store View is not associated with the particular Website, the product will not be displayed in the selection of products available to add to the Listing. Thus, you have two solutions.
- Check whether you have selected the appropriate Website in Magento Product settings. To do that, navigate to Catalog > Manage Products > select Product > Product Information > Websites tab (Magento 1) or Products > Catalog > select Product > Product in Websites section (Magento 2).
- Create a new M2E Pro Listing and specify the required Magento Store View at the General Settings step:
eBay/Amazon/Walmart > Listings > Add Listing button > Step 1: General Settings > Magento Settings section > Magento Store View (Magento 1)
eBay/Amazon/Walmart > Listings > M2E Pro > Add Listing button > Step 1: General Settings > Magento Settings section > Magento Store View (Magento 2)