A new Extension Key must be obtained after Magento is moved to a new server

Extension Key is a unique identifier of M2E Pro that undergoes validation based on the Domain name and IP address. Extension Key is used for security reasons to prevent attacks and inconsistent access to your data. 

If you’ve moved your Magento to a new web server and/or new host with a different IP and/or domain, you need to obtain a new Extension Key for your Module. 

Follow these steps to do it:

1. Sign in to your customer account on M2E Accounts.
2. Open your M2E Pro subscription details by clicking on the card, switch to "Keys" tab, and click "New Key".

To associate the new Key with your current IP/Domain, please complete the steps:

1. Copy the newly generated Extension Key.
2. Paste the Key in the Admin Panel of your Magento: System > Configuration > M2E Pro > Billing Info (for Magento v1.x) or Stores > [Settings] Configuration > M2E Pro > Extension Key (for Magento v2.x).
3. Confirm the changes.
4. Click Save Config at the top of the page.
5. Clear Magento cache: System > Cache Management > Flush Magento cache and Cache Storage (for Magento v1.x) or System > Tools > Cache Management > Flush Magento cache and Cache Storage (for Magento v2.x).