1. Please update CityTours theme to the latest version. You can download latest version from themeforest and replace the them with latest version in your website.
We fixed it in several days ago.
2. , 3 Please confirm your api key is correct and you set currency code correctly. Currency code should be acceptable in paypal such as USD, EUR, etc. You can add currencies in Currencies menu. After added currencies, you should set available currencies and default currency in theme options panel.
If you did them correctly, but have the same error, please send me your website url and admin credentials.
Let me check your website. Please note you should update the theme to the latest version.