Beginning this January, Authorize.net enhanced its login process by enabling multi-factor authentication, which is now required to access your account. This means you will be prompted to enter a one-time passcode that is sent to the email address associated with your Authorize.net username at each login.
After verifying your account, you are provided with the option to remember the login device, which will reduce the additional verification requirement when you login in the future on the same device.
Please make sure your email contact information is up to date so you can complete this process. To learn how to update your email address, read our support article here.