On the order page, VAT number always appears as a row. When the buyer has no VAT number, the value shows as a dash (-). That is expected.
Buyers choose whether they are a VAT-registered business. Practices that provide exempt care and do not reclaim VAT on purchases can buy without a VAT number. Ordentic stores that choice on the order at checkout. Later changes to the buyer’s profile do not change older orders.
You still see shipping and billing details to fulfill and invoice. The purchase agreement stays between you and the practice. If a VAT number is present, use it for your own invoicing and records. If you see a dash, invoice with the company and address details shown.
The same empty value can appear in Supplier API billing address VAT number (null) and in order exports. The new-order email does not include the buyer VAT number at all.
For how Ordentic applies VAT on reverse charge and destination VAT, see How does VAT work for orders via Ordentic.