You will need to link your Noggin Prime Channel subscription to a Noggin account.

This can be done on the newly installed Noggin mobile app for Android or iOS.

Tap "Get Started" to create a new Noggin account or "Sign In" to log into an existing account that doesn't have an active subscription.
 
If you chose "Get Started", after creating your account and setting up your first child profile, choose "Verify Subscription" under "Already have a subscription to Noggin?" > Choose Amazon Channels > Log in to your amazon.com account.
 
Once you are signed in to amazon.com, tap Agree and Connect to Amazon. Check your email and look for an email from Noggin. Tap the verification link to activate your account. Once these steps are completed, you can sign into the Noggin app on any supported device.
 
Alternatively, you can register your account at https://www.noggin.com/amazon. Scroll down and select the blue Connect My Subscription button. Create a Noggin account or Sign In to an existing account that doesn’t have an active subscription. Once you are signed in, tap Agree and Connect to Amazon. You will be sent to the Amazon website to enter your Amazon Prime account information and verify the Noggin channel subscription. Once these steps are completed, you can sign into the Noggin app on any supported device.

Please note, a Noggin App subscription does not give access to the Noggin Channel on the Amazon Prime Video app.