Adding VAT
Download and install Client Meta Framework with VAT to add VAT to your clients.
Please read more about this add-on on it’s Github page, feel free to fork it and add pull-requests.
Custom Client Meta
The add-on is also a great example of how to add new client meta with some example code for creating new metaboxes via the easier to use Sprout Apps APIs.
To add additional meta fields we recommend you copy (or fork) the original add-on. The open SI_Client_Meta and start modifying the code to fit your needs.