Hi!
Thank you for your message! You seem to be using an old version of CalenGoo that uses an old login mechanism that isn't supported by Google any more. They have stopped supporting it
in the past few days. CalenGoo contains the new login method since January 2017.
Please just update CalenGoo. The current version is 1.5.57. You can see your version under "Settings > Info" (in the upper right corner). As usual you can download the update for free from Apple's AppStore using the "AppStore" app.
However you said that you "reinstalled the app" so you should have got the latest version. Are you maybe using an old iOS version? You need iOS 8.0 or newer for the new login mechanism. If you don't have iOS 8.0 or newer please install it. If you don't want to install it the only option is to sync CalenGoo via the iOS calendar with Google Calendar: Add your Google account in the "Settings" app under "Mail, Contacts, Calendars" and then start CalenGoo and turn "Settings > Accounts > Show iPad calendars" on. Or tap "iOS/iCloud" calendars right after installing CalenGoo.
Does that fix it? Please try this and don't hesitate to contact me again if you still have problems or if you have any questions!
Kind regards
Dominique Gunia