How can we improve WHMCS?

When we configure VAT to be validated, if the VAT is invalid, it won't allow the customer to register.
This has tax implications and unnecessary extra configurations.
Let me explain.

We need to save the customer's NIF, TIN, or identification document. For that, we can easily rename the VAT field. However, if we enable verification, the tax_id field only allows the data to be recorded if the VAT verification is positive. This means we need to create a custom field to do exactly what we need: collect the identification data of the customer who doesn't have a valid VAT.

It would be as simple as allowing the data to be recorded even if the VAT verification is enabled. Only if the VAT is valid would the tax exclusion work. However, if it's invalid, the data is still recorded in the database, and the customer will not be exempt.

There could be a checkbox to decide whether or not to use this option, but right now I'm forced to have two fields, and this confuses many customers. Right now we need to have one field for VAT and another for customers who don't use VAT.