In account settings, in 3rd party listings tab, the option Import 3rd Party Listings IS ENABLED, see attachment.
Technical support answered me that CRON must be enabled. In my case there was not any cron job in server environment.
=================================From technical support email:========================================
"We've investigated the issue and it turns up Cron Job is not running for your M2E. That is the reason 3rd Party Listings does not import to M2E. Starting from the 6.1.1. version for Magento v 1.x and all versions from Magento v 2.x M2E Pro uses it's own Cron Service."
Now I have activated Cron Job every minute (perhaps now cron is too frequent?) but I cannot see any products syncronized whenever I see at Listings > 3rd Party Listings tab.
Anyone has idea how to solve?