Both i.e. ‘Active’ and ‘Activate’ represent your account status. As you know that you can add multiple accounts per service, but can upload to only one account at a time. So, when you click ‘upload’ button, it will be uploaded to the account which has ‘active’ status.
In the image below, there are three Dropbox accounts. The first one has active status whereas 2nd and 3rd have ‘activate’ status. When you upload photos, they will be uploaded in first account. If you wish to upload photos to second account, simply click on ‘activate’ and the status will change to ‘active’ and then follow the usual photo upload process.