The Mojio sandbox environment has been deprecated. There is now just the Mojio Live Developer Centre.
A shiny new sandbox key has been issued to each of your production level developer account applications.
There are three sitations you might find yourself:
You have only a "Sandbox Server" account created and not a "Live Server" account.
In this case you need to:
Create a new account at developer.moj.io where you will be issued a key.
Your Sandbox server account is no longer available.
You have only a "Live Server" account. Yeah! You don't need to create an account just use the provided key,
You have both "Live Server" and "Sandbox Server" accounts. All your Sandbox server accounts are no longer available.
Fear not, your Live account now has all the data you need.
Note that you may need to edit or recreate your application on the ""Live Server"" to match what you were doing in the "Sandbox Server"".