This may be because you've either synced the wrong Google account (instead of the one you use to log in to AdWords/ MCC), or because you have entered an incorrect customer ID.
Firstly, please double check that you have entered the correct customer ID. Your customer ID can be found here:
Still not working?
It looks like you have synced WeatherAds with the wrong Google account. WeatherAds must be synced with the Google sign in used to manage your AdWords (or MCC account. You will need to de-sync AdWords in WeatherAds and then re-sync AdWords using the correct Google login. Please follow the steps outlined below to do this:
Go to this page: http://app.weatherads.io/Manage/AdPlatforms and de-authorize AdWords. (hit ‘remove’ button next to AdWords)
Once this is done, please go to https://myaccount.google.com/permissions and check if WeatherAds is listed in there. If it is, please remove it from your apps. Please make sure you are signed in with the correct Google account when you are performing this step!
Once you have completed these steps please return to this page: http://app.weatherads.io/Manage/AdPlatforms and re-authorize your AdWords account. Then enter the customer ID associated with that AdWords account. Please ensure it is the correct customer ID.