I got message: "For security reasons, please log in again"

You need to re-get token for eBay account in m2e pro.

Please, go to Configuration > Accounts > General TAB, click on the Get Token button. (You will be redirected to the eBay website.) Sign-in and press I Agree on eBay page. Do not forget to press Save button after returning back to Magento.

Please let us know if you find this information inaccurate