Problem by upgrading from Basic to "Pro"

Sorry, my English is not perfect....

During the process for upgrading the Zoom -Tarif from Basic to Pro it is necessary to notice a certain "tax-number".

(in Germany it is the so-called "USt-Nr." (similar to VAT)).

I notice my right number, but always the answer is: " number not valid".

(but no writing-mistake).

What could be the problem?

(very little company)

The "chat" from Zoom was not able to help (10 trials).

Have anybody an idea, where could be the key?

Many thanks.

Rainer