Authorisation PC - e-books Google Play

I tried to authorise my computer (WIN 10) to access the e-books that I bought in Google Play (I want to transfer the books to my KOBO H2O e-reader).

- I used as vendor login-id: my Gmail e-mail adress

- I used as vendor password: my Gmail password

I get the error: Wrong id/password for this E-book vendor. Try again

Can somebody help me? Thanks