I haven't the 3 files: /assets/google-...

[santiagos5]

Obtain the credentials (as already described above) and add them in the files:
./assets/google-client-secret.json
./assets/google-access-tokens.json
./assets/google-private-key.json (The OAuth2 certificate file you downloaded and saved.)

I haven't this files in my assets folder, only config.txt file