ITR-U for non taxable income

I think you have to pay penalty 

But sir, I do not have taxable income then why income tax department is sending me repeated emails to file ITR-U? I don't understand. One of my friend doesn't have any entry in the AIS for FY2021-22, till he is receiveing email to submit ITR-U.

Itr u is applicable for persons who has not filed returns for consecutive 2 years.

It is last oppurtinity to file ITR,  ITRU for fy-2021-22 after 31-mar-2025 we can't file ITR,
Yes, you have to pay penalty Rs.1k upt 5L income and above 5L will be pay Rs.5k.
Nil ITR not allowed to file, Nil Means income are under exemption limit 

My income is under exemption limit till I am getting emails/SMSs to file ITR-U? Why?

Due to limit of time you are getting emails/SMS.It's last chance to file itrU for the period of AY-2022-23