From 18th July 2019 Premium + was discontinued. Any subscriber that has a Premium + subscription via in-app purchase with the Amazon app store needs to cancel their subscription and set up and new Premium subscription.
To cancel your Amazon Premium + subscription for TVPlayer:
1. Please visit: www.amazon.co.uk/appstoresubscriptions
2. Sign in using your Amazon credentials
3. Manage your subscription (example Appstore can be seen below)
To set up a new Premium subscription for TVPlayer:
Log into the TVPlayer website here: https://tvplayer.com/registration/plans?nrsrc=nav&nrc=tp and purchase a new Premium Subscription.