Since 1 October 2022, My Tax Authorities require an additional SMS check to be able to log in with a DigiD username and password.
It is possible to log in to Mijn Belastingdienst in various ways, such as with the DigiD app and with DigiD username and password. To protect personal data even better, from October 1, 2022, an additional SMS check will be required for logging in with DigiD username and passwords. You then log in with DigiD username and password and an extra SMS check. This SMS code is sent to the telephone and must be used when logging in.
Source Taxence
