Validate Swiss TVA

[carlos-spherag]

It does not allow me to validate the Swiss tva, the error is:
"input string was not in a correct format".
My code:

When I enter the same data in the demo validator it works, where can I check the format of the string I have to pass to the "CountryValidator" method?
https://randommer.io/SocialNumber/VatValidator

Doc format:
CHE-xxx.xxx.xxx TVA