@matt_b_london some of our clients have received the same notification and I also checked the difference to Shopify Basic Tax.
It seems like Shopify Tax automates some process depending on product types the market settings.
https://help.shopify.com/en/manual/taxes/us/choose-tax-service
Did you, by any chance, use the invoicing tool provided by Shopify tax?
From my understanding, Basic Tax will also handle VAT at checkout, just not automated by product type.