Product is not Listed. The process of New ASIN/ISBN creation has been started, but the Variation Theme was not set. Please, set the Variation Theme to list this Product

Please define by which option(s) your product will vary on the Amazon website, i.e. Variational Theme, and set the correspondence between Magento and Amazon variation attributes. To do it, please navigate to M2E Pro Listing and click Manage Variations next to the relevant Listing Product. Once it is done, you can apply the List action.