When signing in to MailBluster, if the screen below pops up, instead of typing a random OTP code, just click Cancel. You will then be asked to enter the OTP code again, and a new email with a new OTP code will be sent to your email address.
You will receive a new OTP code as shown below. Enter the new OTP code exactly and you will be able to sign in to MailBluster. Please note: Every OTP code expires after 10 minutes of receiving it in inbox of your registered email.