Support for application versions has been removed in Backendless v4. As an alternative to versions, it is recommended to create multiple copies of the same application and export/import data between the apps. As a result of the version support removal, application initialization in the code does not require version name in the
Backendless.initApp( applicationID, secretKey, versionName );
Backendless.initApp( applicationID, apiKey );
Notice that version 5 uses the term "API key" for the concept we used to call "secret key".