Is this what you were referring to? – see the screenshot below. If yes, Amazon has always been very strict against sellers NOT USING external URL or links which take them off Amazon but we’ve tended to be okay if it was an Amazon link.
The Automated “Ask for Review” is a very good tool but when a buyer posts Seller Feedback, sometimes they assume it is being posted as a Product Review, so you may miss them converting it.
If you are risk-averse, you may decide to change your verbiage in your email to offer a step by step process of how the customer can find ‘Your Account > Your Orders’ and find the product name and add their review directly through their amazon.com account.