When the requests are submitted to Channel servers, the responses are not received immediately. This is due to Channel systems peculiarity. For example, to get a response from Amazon API, M2E Pro needs to constantly check if the requests are processed. Since this Channel API use a queue system: all sent requests are queued and processed on “first come, first served" basis.
Besides, to perform the tasks on eBay/Amazon (e.g., quantity and price updating, orders importing/creation etc.), the permanently working automatic synchronization is required. This process is provided by M2E Pro Cron Service that works as a background mechanism for a constant script running.
If any problems as for automatic synchronization occur, please follow our recommendations:
For M2E Pro versions 6.1.1 or higher for Magento v 1.x and all M2E Pro versions for Magento v 2.x, no particular settings for automatic synchronization are required. Yet, if you have any related questions, contact M2E Pro Support at email@example.com.
Alternatively, you can set Magento Cron. In this case, automatic synchronization will be performed based on Magento Cron job settings. This configuration can also be helpful in case M2E Pro Cron Service execution temporary fails. Since Magento Cron will trigger the tasks until M2E Pro Cron Service is restored. Check this post to learn how to set Magento Cron.
If the automatic synchronization is still not performed, read the article for the details on how to resolve the problem.