mTAN stands for mobile transaction authentication number. An mTAN is sent via SMS and acts as an extra layer of security verification to authorise your transaction.
Before sending money from your Nuri user account, you will receive an SMS with an mTan to your registered mobile number.
Each mTan is valid for two minutes. If you exceed these two minutes from the time you received the text message, you will get a warning message and must begin the transaction process again. If you do not enter the mTan on time, your transaction will not be processed.