You should be able to see the black graphic below on just about any webpage in the Kindle Store. Click on the banner and you will see the second image below telling you that your offer has been activated.

To receive the promotional credits, you must: (1) activate the offer by clicking on “Get offer” at any time before 11.59pm (BST) on 11 June, 2020 and (2) spend £10 or more on any one or more Kindle Books before 11.59pm (BST) on 11 June, 2020.

Limited-time offer. Terms and conditions apply.

If you cannot find the offer, then try clicking here