Usually, the CVV number is required in order to complete a payment, however, the rules whether the CVV number field is mandatory or not can vary based on the issuing bank, card provider, and your payment gateway settings. For example, many banks approve transactions even if the CVV doesn’t match what they have on file or Maestro cards do not typically include a CVV at all.
We would recommend that you check your Braintree settings to see if you currently allow transactions without the CVV number. This can be found under Settings > Processing > Fraud Tools > CVV Options.
For more information please see this support article here from Braintree where all the rules and exceptions are explained.