Please check the M2E Pro versions lifecycle policy before installation/upgrading to be sure your Magento version is compatible with the latest M2E Pro version.
M2E Pro extension integrates Magento into eBay, Amazon, and Walmart platforms to deliver the multi-channel retail experience that boosts your profitability.
The Solution supports multiple eBay/Amazon/Walmart accounts, and continuous inventory synchronization with full order lifecycle management across 23 eBay, 14 Amazon, and 2 Walmart marketplaces.
The Module is improved on a constant basis to provide you with the highest level of service. Detailed information about each version can be found in the Release Notes/Policy section. It is strongly recommended to use the most up-to-date version.
No data can be lost during an upgrade process. However, please, always back up your system prior to any upgrade-related activity.
via Connect Managervia M2E Pro Updaterfrom Source Code Archivevia ComposerTypical causes of failed upgrade