When a file closes and a client provides us with glowing feedback, we respond by thanking them for their feedback and asking them to provide a Google rating or review. We have been doing this for about a month, and so far no one has provided any reviews or ratings. Likewise, we previously had customer survey at the end of files (to establish a NPS), but no one completed them... Are there magic words or a better time in the process to improve engagement?
I agree with a couple of other answers in that it will depend on the nature of the business and even more specifically the business (and your audience).
So I would recommend you embark on a process of testing different times, email subject lines and messages, review platforms, etc. But document the tests to make sure you understand what is working.
Best practices are a good start to begin testing what gets you results.
As a couple of other answers suggested, providing a direct link to write a review will help. To do this you can create your own Google review link here - https://www.onqmarketing.com.au/google-review-link-generator/.
I would also be careful with how you're asking for reviews and understand that different platforms have different guidelines. For example, Yelp does not like you to solicit and Google definitely doesn't want you paying or compensating for reviews.