Slow Horses Season 4

Resubscribed on iPhone, scanned QR code on TV, streaming device on TV is Amazon Firestick.

That seems correct and should work. Alternatively to using the QR code, sign in manually by typing in the Apple ID and password.

Everytime I subscribed by clicking on "Get Apple TV+" or "Come Back to Apple TV" link it sun and the tick in a circle / Done appeared - but the subscription at £8.99 hasn't been taken.

1. See if this subscription is listed as active on your iPhone: See your subscriptions overview - Apple
2. If it is, then next see if you can stream Apple TV+ content in the TV app on iPhone.
3. If the previous step was successful, then open the Apple TV app on Fire TV, sign in with the same Apple ID as in use on your iPhone, then try watching an Apple TV+ show.

If you don’t see the Apple TV+ subscription listed as active in your subscriptions overview on iPhone, then you may benefit from some assistance from the Apple Support staff. They should be able to see if anything is blocking the subscribe routine. Contact Apple for support and service (phone numbers) or start your support request online (chat/​email/​callback).

On what device do you have the Apple TV app, through which you trying to watch this Apple TV+ show?

Is this on a smart TV, or TV with an external streaming device? What smart OS platform?

On what (other) device did you (re-)start the subscription?

Did you manage to sign in to the Apple TV app, through the in-app Settings, using the Apple ID account to which the Apple TV+ subscription is linked? Then any active subscription would be applied, and you wouldn’t get the How to Watch blurb.