It's easy to get confused by what is meant by the various different accounts used in apps and websites nowadays. This article tries to explain the differences between the accounts you use with our apps.
If you have an email address at which you are able to receive email, then that is an email account. You might, for example, have a GMail account or a Yahoo Mail account.
Many websites, apps and other online services allow you to use your email address as a User ID when creating other user accounts. For example, with The Photographer's Ephemeris, you can create a Crookneck Photo Apps account to use with certain features within the app such as Location Synchronization. In this case, your email address is your username or user ID, and the Crookneck Photo Apps account is a separate account to your original email account.
Therefore, it's quite possible that when using our apps, you may have both a Crookneck Photo Apps account and an Apple ID/Google Account.
These might well have (probably should have) different passwords.
If you wish to re-download a previously purchased app, you'll need the Apple ID or Google Account details.
If you want to sign in to your account with TPE, you'll need the Crookneck Photo Apps account details.
We strongly recommend you avoid using multiple Apple IDs and Google Accounts. Apps are tied to the account used to make the purchase. If you switch accounts, you won't easily be able to reinstall or update the apps purchased under the other account, and in-app purchases may not work.
Instead of creating a new Apple ID, for example, you should look to change the email associated with the existing account, as described here: https://support.apple.com/en-us/HT202667