The eBay Sandbox is a virtual environment that replicates the live eBay Production environment. Sandbox provides functionality for testing purposes with no effect on any live eBay products and services.
Testing in the eBay Sandbox allows simulating listing the items, completing sales transactions without paying real fees to eBay, and without having any obligation to deliver real items to real buyers.
In order for M2E Pro to interact with your eBay account, you need to generate a user token. It identifies you as an eBay member and proves that you give M2E Pro permission to operate with your eBay data (such as user information and account data) on your behalf.
How to generate user token in M2E Pro:
1) Go to eBay > Configuration > Accounts > Add account
2) Enter the Title of your eBay account.
3) Select Sandbox (Test) environment and click Get Token.
4) Sign in to your eBay Sandbox account.
5) Click Agree on the ‘Grant application access: M2E Pro’ page.
Once done, the token will be generated and you will see Yes status near the Activated field.
6) Click Save and Continue Edit to save the changes.