For EU customers the VAT number can be added during signup. In that case the country code should not be added for the number (that is the first two letters before the number).
The format for the EU VAT numbers are as follows:
VAT identification number structure
Member State Structure Format*
AT-Austria ATU99999999 1 block of 9 characters
BE-Belgium BE0999999999 1 block of 10 digits
BG-Bulgaria BG999999999 or
BG9999999999 1 block of 9 digits or1 block of 10 digits
CY-Cyprus CY99999999L 1 block of 9 characters
CZ-Czech Republic CZ99999999 or
CZ999999999 or
CZ9999999999
1 block of either 8, 9 or 10 digits
DE-Germany DE999999999 1 block of 9 digits
DK-Denmark DK99 99 99 99 4 blocks of 2 digits
EE-Estonia EE999999999 1 block of 9 digits
EL-Greece EL999999999 1 block of 9 digits
ES-Spain ESX9999999X4 1 block of 9 characters
FI-Finland FI99999999 1 block of 8 digits
FR-France FRXX 999999999 1 block of 2 characters, 1 block of 9 digits
GB-United Kingdom GB999 9999 99 or
GB999 9999 99 9995 or
GBGD9996 or
GBHA9997 1 block of 3 digits, 1 block of 4 digits and 1 block of 2 digits; or the above followed by a block of 3 digits; or 1 block of 5 characters
HR-Croatia HR99999999999 1 block of 11 digits
HU-Hungary HU99999999 1 block of 8 digits
IE-Ireland IE9S99999L
IE9999999WI 1 block of 8 characters or 1 block of 9 characters
IT-Italy IT99999999999 1 block of 11 digits
LT-Lithuania LT999999999 or
LT999999999999 1 block of 9 digits, or 1 block of 12 digits
LU-Luxembourg LU99999999 1 block of 8 digits
LV-Latvia LV99999999999 1 block of 11 digits
MT-Malta MT99999999 1 block of 8 digits
NL-The Netherlands NL999999999B998 1 block of 12 characters
PL-Poland PL9999999999 1 block of 10 digits
PT-Portugal PT999999999 1 block of 9 digits
RO-Romania RO999999999 1 block of minimum 2 digits and maximum 10 digits
SE-Sweden SE999999999999 1 block of 12 digits
SI-Slovenia SI99999999 1 block of 8 digits
SK-Slovakia SK9999999999 1 block of 10 digits
Remarks:
*: Format excludes 2 letter alpha prefix
9: A digit
X: A letter or a digit
S: A letter; a digit; “+” or “*”
L: A letter
Remarks:
For the check, the service of the EU is used. You can check your own VAT number here: http://ec.europa.eu/taxation_customs/vies/vatRequest.html
The format of the VAT number for all EU countries can be found here: http://ec.europa.eu/taxation_customs/vies/vatRequest.html (and than Q11).