Java code error building dex in console

Hi,
I can’t integrate StartApp’s SDK for unity, all the time this error appears and I don’t know what I did wrong. I follow all the steps from a tutorial, I am using the same version of the program and still. Does anyone have any idea about this error ? How can this be solved ?
Thanks !

Building DEX Failed!
Failed to complete Java code to DEX. See the Console for details
