0 rate/no tax based upon VAT number

Hi there,
For this shop based in the Netherlands there are also Belgium buyers.. some of them are business as well and want to order without VAT/tax.
How can i set this to no tax/zero rate once the enter their VAT number at the checkout?

For example: The VAT/tax field is optional but once they fill it in they get the option to order tax free.

Thank you very much in advance!

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