Tax Configuration - Validate Tax-ID when possible
At this moment (WHMCS 7.7 RC1) customers are able to send fake information in the TAX-ID/VAT-ID field. For most of the European Countries, it is easy and simple to validate the format of the Tax-ID ( Example: https://formvalidation.io/guide/validators/vat/ / https://ec.europa.eu/taxation_customs/tin/tinRequest.html / https://ec.europa.eu/taxation_customs/tin/tinByCountry.html).
It doesn't need to validate via webservice, but is essential to validate the format. This validation will prevent someone to fill the field with invalid/false information that will then not be valide for usage in a external certified billing software.