Payment rails
IBAN
International bank account identifier carrying check digits that catch typing errors.
An IBAN starts with a two-letter country code, followed by two check digits, then the national account identifier. Its length varies by country: 27 characters in France, 22 in Germany, 16 in Belgium. A form accepting only one length is defective.
The two check digits are verified with a modulo 97 calculation: a typo is caught mathematically, without querying the bank. That calculation says nothing about whether the account exists or who holds it. A perfectly valid IBAN can point at a closed account; the transfer will leave and bounce back a few business days later.