For those of you still stuck on this… When you reach the sign-in page and click “Sign In with Epic Games”, just put your Google email and Google password in the ‘Email’ and ‘Password’ sections. DON’T click on the Google logo and sign in that way. I did that, and it worked for me 
after many attempts of 'code ’ must be a string. Hope this helps. Thanks to @turcoasmilo
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