If you are using Postcode Anywhere / PCA Capture from Logate with Dynamics 365 and are failing to see the Address Validation appear when clicking into the Address Fields for a Lead, Contact or Company – then you can click F12 to open the Chrome/IE Developer Console and see the error that is being returned.
If this error looks like:

Then there is a simple reason why this is failing.
The Script for PCA Capture relies on certain elements in the DOM of the CRM Form, and these elements are only present if Legacy Form Rendering has been deactivated.
So to fix the problem, navigate to System Settings in CRM and ensure that Use Legacy Form Rendering is set to NO.

With this done, we should see the Address Validation working as we would expect:

Legacy Form Rendering could often be a handy tool (particularly before the Service Releases for Dynamics v8.2) to help backwards compatibility after upgrading Dynamics from earlier versions – but now can usually be deactivated to help Scripts such as PCA work as expected.
Further information on the PCA Capture tool for address validation can be found here: https://www.loqate.com/en-gb/address-verification/address-capture/
This helps to match to a full validated address by connecting the Dynamics 365 data entry to the Royal Mail Address API in the UK, and other Open Data Sources for countries around the world.