Please specify the product's option(s)

This message means, that there’s no information about options, which is required to create Magento order. For example: the Magento configurable product was listed on eBay ignoring variations(as a simple), so eBay order does not have required options and Magento fails to create order for the item.

Another reason can be change of the option label. For example: configurable product had the option with name “Color” and with such name it was listed on eBay. Later the name was changed to “Item Color”, so the name of options(variations) on eBay and in Magento are different.

To create order, you should set up option, go to Sell On eBay -> Sales in M2E Pro for M1 and in eBay Integration > Sales > Order in M2E Pro for M2 , click on the necessary order and use Set Options functionality: http://docs.m2epro.com/x/LgAJAQ and http://docs.m2epro.com/x/awItAQ

eBay Integration