There are two possible reasons you are receiving this authorization error message:
First, please check to make sure that you're using the correct username/email/password when you are prompted to login to Fitbit to grant permission to Count.It. The error being returned says "Invalid Credentials," and that suggests that you may be using the wrong user/pass combination. Keep in mind, this user/pass is the one you use to log in to your Fitbit app.
Second, when connecting your Fitbit to Count.It, Fitbit provides the option to grant permission to two types of data: "Profile" and "Activity & Exercise." In order to successfully connect, you must grant permissions for both. In other words, click "Select All" in the image below:
A few important things to note:
The only thing we collect in your Fitbit "profile" is your avatar image, which you can change any time on Count.It.
For activity and exercise, we only collect and use your step and cycling data. We do not collect any other data gathered or stored on your Fitbit app, including detailed exercise data, calories, weight, etc.