OMB Cloud validates tax IDs against the format and checksum expected by each country. Common errors below.
Mexico (RFC)
RFC for natural persons is 13 chars (4 letters + 6 digits + 3 alphanumeric); for legal entities is 12 chars (3 letters + 6 digits + 3 alphanumeric). Spaces, dashes and lowercase letters fail validation. Strip whitespace and uppercase before saving.
Spain (NIF / CIF)
NIF is 9 chars: 8 digits + 1 letter (check digit). CIF is similar but starts with a letter that indicates entity type. If the check digit doesn't match the algorithm, validation fails. Verify with the AEAT website.
USA (EIN)
EIN is 9 digits in the format XX-XXXXXXX. Either format (with or without dash) is accepted. If the prefix is invalid (some prefixes aren't assigned), validation fails.
Brazil (CNPJ)
CNPJ is 14 digits with check digits. The format is XX.XXX.XXX/XXXX-XX. Random 14-digit strings fail the check-digit validation. Use Receita Federal's public API to verify if in doubt.
If the tax ID is correct but validation fails
Three possibilities: (1) you typed it wrong (re-check digit by digit), (2) OMB Cloud is offline from the tax authority service (try again in 30s), (3) the entity is new and not yet in the tax authority database (uncheck "Validate against tax authority" and save manually).